Include <icon> element in nuspec files

This commit adds the nuget-icon.png file to each of the nuspec files,
referencing this file within the <icon> element. This change is in line
with Nuget recommendations.

(cherry picked from commit e5147c3)

Author: russcam

build/Elasticsearch.Net.VirtualizedCluster.nuspec

@@ -9,6 +9,7 @@
 		<license type="file">license.txt</license>
 		<projectUrl>https://github.com/elastic/elasticsearch-net</projectUrl>
 		<iconUrl>https://raw.githubusercontent.com/elastic/elasticsearch-net/master/build/nuget-icon.png</iconUrl>
+		<icon>images\nuget-icon.png</icon>
 		<requireLicenseAcceptance>false</requireLicenseAcceptance>
 		<summary>Provides a way to assert client behaviour through a rule engine backed VirtualClusterConnection</summary>
 		<description>Provides a way to assert cluent behaviour through a rule engine backed VirtualClusterConnection</description>
@@ -27,6 +28,7 @@
 	</metadata>
 	<files>
 		<file src="..\license.txt" target="" />
+		<file src="nuget-icon.png" target="images\" />
 
 		<file src="output\Elasticsearch.Net.VirtualizedCluster\netstandard2.0\Elasticsearch.Net.VirtualizedCluster.dll" target="lib\netstandard2.0"/>
 		<file src="output\Elasticsearch.Net.VirtualizedCluster\netstandard2.0\Elasticsearch.Net.VirtualizedCluster.pdb" target="lib\netstandard2.0"/>

build/Elasticsearch.Net.nuspec

@@ -9,6 +9,7 @@
 		<license type="file">license.txt</license>
 		<projectUrl>https://github.com/elastic/elasticsearch-net</projectUrl>
 		<iconUrl>https://raw.githubusercontent.com/elastic/elasticsearch-net/master/build/nuget-icon.png</iconUrl>
+		<icon>images\nuget-icon.png</icon>
 		<requireLicenseAcceptance>false</requireLicenseAcceptance>
 		<description>Elasticsearch.Net</description>
 		<summary>Exposes all the Elasticsearch API endpoints but leaves you in control of building the request and response bodies. Comes with built in cluster failover/connection pooling support.</summary>
@@ -31,6 +32,7 @@
 	</metadata>
 	<files>
 		<file src="..\license.txt" target="" />
+		<file src="nuget-icon.png" target="images\" />
 
 		<file src="output\Elasticsearch.Net\netstandard2.0\Elasticsearch.Net.dll" target="lib\netstandard2.0"/>
 		<file src="output\Elasticsearch.Net\netstandard2.0\Elasticsearch.Net.pdb" target="lib\netstandard2.0"/>

build/NEST.JsonNetSerializer.nuspec

@@ -9,6 +9,7 @@
 		<license type="file">license.txt</license>
 		<projectUrl>https://github.com/elastic/elasticsearch-net</projectUrl>
 		<iconUrl>https://raw.githubusercontent.com/elastic/elasticsearch-net/master/build/nuget-icon.png</iconUrl>
+		<icon>images\nuget-icon.png</icon>
 		<requireLicenseAcceptance>false</requireLicenseAcceptance>
 		<description>NEST uses an internal serializer. This package enables serialization for your documents using your own custom Json.NET serializer</description>
 		<summary>NEST uses an internal serializer. This package enables serialization for your documents using your own custom Json.NET serializer</summary>
@@ -29,6 +30,7 @@
 	</metadata>
 	<files>
 		<file src="..\license.txt" target="" />
+		<file src="nuget-icon.png" target="images\" />
 
 		<file src="output\Nest.JsonNetSerializer\net461\Nest.JsonNetSerializer.dll" target="lib\net461"/>
 		<file src="output\Nest.JsonNetSerializer\net461\Nest.JsonNetSerializer.pdb" target="lib\net461"/>

build/NEST.nuspec

@@ -11,6 +11,7 @@
 		<license type="file">license.txt</license>
 		<projectUrl>https://github.com/elastic/elasticsearch-net</projectUrl>
 		<iconUrl>https://raw.githubusercontent.com/elastic/elasticsearch-net/master/build/nuget-icon.png</iconUrl>
+		<icon>images\nuget-icon.png</icon>
 		<description>Strongly typed interface to Elasticsearch. Fluent and classic object initializer mappings of requests and responses. Uses and exposes Elasticsearch.Net</description>
 		<summary>Strongly typed interface to Elasticsearch. Fluent and classic object initializer mappings of requests and responses. Uses and exposes Elasticsearch.Net</summary>
 		<releaseNotes>https://github.com/elastic/elasticsearch-net/releases/tag/$version$</releaseNotes>
@@ -27,6 +28,7 @@
 	</metadata>
 	<files>
 		<file src="..\license.txt" target="" />
+		<file src="nuget-icon.png" target="images\" />
 
 		<file src="output\Nest\net461\Nest.dll" target="lib\net461"/>
 		<file src="output\Nest\net461\Nest.pdb" target="lib\net461"/>