Use version var in gradle file. Upgrade gradle version to 4.0 (#23)

Author: imanushin

build.gradle

@@ -51,8 +51,8 @@ bintray {
         licenses = ['Apache-2.0']
         vcsUrl = 'https://github.com/MicroUtils/kotlin-logging'
         version {
-            name = "1.4.5"
-            desc = "kotlin-logging 1.4.5 - Lightweight logging framework for Kotlin"
+            name = version
+            desc = "kotlin-logging $version - Lightweight logging framework for Kotlin"
             released  = new Date()
         }
     }
@@ -113,13 +113,13 @@ publishing {
         MyPublication(MavenPublication) {
             pom.withXml {
                 def root = asNode()
-                root.appendNode('description', "kotlin-logging 1.4.5 - Lightweight logging framework for Kotlin")
+                root.appendNode('description', "kotlin-logging $version - Lightweight logging framework for Kotlin")
                 root.children().last() + pomConfig
             }
             from components.java
             groupId 'io.github.microutils'
             artifactId 'kotlin-logging'
-            version "1.4.5"
+            version version
 
             artifact sourcesJar
             artifact javadocJar

gradle/wrapper/gradle-wrapper.properties

@@ -3,5 +3,5 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.13-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.0-all.zip
 kotlin.incremental=true