Fix Signature test

Type .toString returns values that look like:
android.widget.TextView.SavedState
but current.txt equivalent looks like:
android.widget.TextView$SavedState.

A simple find/replace makes the .toString compatible with what is
found in current.txt.

bug:18236689
Change-Id: I8041bb4017cace3968d14fbe21003f73640589dc
(cherry picked from commit 279ee630)
(cherry picked from commit ab5596b1)