Fix name of nightly build.

app/build.gradle

@@ -268,7 +268,7 @@ android {
             ext.websiteUpdateUrl = "null"
             buildConfigField "boolean", "PLAY_STORE_DISABLED", "false"
             buildConfigField "String", "NOPLAY_UPDATE_URL", "$ext.websiteUpdateUrl"
-            buildConfigField "String", "BUILD_DISTRIBUTION_TYPE", "\"internal\""
+            buildConfigField "String", "BUILD_DISTRIBUTION_TYPE", "\"nightly\""
         }
 
         study {