Use "git describe" because it supplies both the commit ID as well as the number of commits since the last release.

app/build.gradle

@@ -122,7 +122,7 @@ task filterAbout {
         into 'src/main/assets'
         filter(ReplaceTokens, tokens: [versionname: android.defaultConfig.versionName,
                                        versioncode: android.defaultConfig.versionCode.toString(),
-                                       commit: "git rev-parse HEAD".execute().text[0..6]])
+                                       commit: "git describe".execute().text])
     }
 }