Fixed missing changes in the version bump to alpha6

buildSrc/version.properties

@@ -1,4 +1,4 @@
-elasticsearch     = 5.0.0-alpha5
+elasticsearch     = 5.0.0-alpha6
 lucene            = 6.1.0
 
 # optional dependencies

qa/backwards-5.0/build.gradle

@@ -18,6 +18,6 @@ integTest {
   cluster {
     numNodes = 2
     numBwcNodes = 1
-    bwcVersion = "5.0.0-alpha5-SNAPSHOT" // this is the same as the current version until we released the first RC
+    bwcVersion = "5.0.0-alpha6-SNAPSHOT" // this is the same as the current version until we released the first RC
   }
 }