build: for the git hash length to 8

avoids inconsistency between different build systems, and fixes
the hash check.

Clover/app/build.gradle

@@ -6,7 +6,7 @@ apply plugin: 'com.android.application'
 def getCommitHash = { ->
     def stdout = new ByteArrayOutputStream()
     exec {
-        commandLine 'git', 'rev-parse', '--short', 'HEAD'
+        commandLine 'git', 'rev-parse', '--short=8', 'HEAD'
         standardOutput = stdout
     }
     return stdout.toString().trim()