Updated version string to 3.0.0.b

Test Plan:
- unit tests

Revert Plan:
- safe

Tags:

Reviewers: mingfli

Reviewed By: mingfli

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D605143

Author: Michael Marucheck

facebook/src/com/facebook/FacebookSdkVersion.java

@@ -23,7 +23,7 @@ public final class FacebookSdkVersion {
     /**
      * The build version string of this SDK.
      */
-    public static final String BUILD = "2.9.9.custom";
+    public static final String BUILD = "3.0.0.b";
 
     /**
      * The migration bundle string with which this version of the SDK was tested.