proguard: keep stacktrace line numbers

Change-Id: Ib851b1b290985dd13ffcff86f6463ce4b9937293
diff --git a/ring-android/app/proguard-rules.pro b/ring-android/app/proguard-rules.pro
index b0e7c51..d41bd53 100644
--- a/ring-android/app/proguard-rules.pro
+++ b/ring-android/app/proguard-rules.pro
@@ -4,6 +4,10 @@
 
 -keepattributes InnerClasses
 
+# To be able to see line numbers in stack traces
+-renamesourcefileattribute SourceFile
+-keepattributes SourceFile,LineNumberTable
+
 -keep class android.support.v7.widget.LinearLayoutManager { *; }
 -keep,includedescriptorclasses class androidx.core.content.FileProvider { *; }