Bump Spine version to 0.7.0.

Author: Alex Tymchenko

build.gradle

@@ -32,7 +32,7 @@ buildscript {
     ext {
         guavaVersion = '20.0'
         protobufGradlePluginVerison = '0.8.0'
-        spineVersion = '0.6.16-SNAPSHOT'
+        spineVersion = '0.7.0'
         //TODO:2016-12-12:alexander.yevsyukov: Advance the plug-in version together with all the components and change
         // the version of the dependency below to `spineVersion` defined above.
         spineProtobufPluginVersion = '0.6.6-SNAPSHOT'