Make ExternalSoMapping public (#130)

Summary:
Pull Request resolved: #130

This class is currently package private and we can't easily access it from React Native.

Reviewed By: cipolleschi

Differential Revision: D62444505

fbshipit-source-id: 554060e5878325f7cd0f1935afb4e328ea7bc0df

java/com/facebook/soloader/ExternalSoMapping.java

@@ -24,7 +24,7 @@
  * provide their own mapping from Open Source.
  */
 @ThreadSafe
-interface ExternalSoMapping {
+public interface ExternalSoMapping {
   @Nullable
   String mapLibName(String preMergedLibName);