add some proguard rules for keeping line numbers

app/proguard-rules.pro

@@ -1,17 +1,2 @@
-# Add project specific ProGuard rules here.
+-renamesourcefileattribute SourceFile
-# By default, the flags in this file are appended to flags specified
+-keepattributes SourceFile, LineNumberTable
-# in $ANDROID_HOME/tools/proguard/proguard-android.txt
-# You can edit the include path and order by changing the proguardFiles
-# directive in build.gradle.
-#
-# For more details, see
-#   http://developer.android.com/guide/developing/tools/proguard.html
-
-# Add any project specific keep options here:
-
-# If your project uses WebView with JS, uncomment the following
-# and specify the fully qualified class name to the JavaScript interface
-# class:
-#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
-#   public *;
-#}