Changed the version of the guava plug-in to 15.0.

This commit fixes issue #31.

The problem that Eclipse picked up an older version of Guava that caused a
`NoSuchMethodError` exception because the older version didn't
Iterables.tryFind(...) method. As a result, Eclipse failed to create the
CompatibilityView object. The lesson here is that I should've paid closer
attention to all exceptions not only the first one in the error log because the
root cause was captured by the second exception.

Author: reprogrammer

plugins/com.google.guava/META-INF/MANIFEST.MF

@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: com.google.guava
 Bundle-SymbolicName: com.google.guava
-Bundle-Version: 1.0.0
+Bundle-Version: 15.0.0
 Bundle-ClassPath: guava-15.0-sources.jar,
  guava-15.0.jar
 Export-Package: com.google.common.annotations,