[libpng16] Fix version numbers in ANNOUNCE

ANNOUNCE

@@ -25,7 +25,7 @@ Other information:
 
 Changes since the last public release (1.6.27):
 
-Version 1.6.28beta01 [January 3, 2017]
+Version 1.6.28rc01 [January 3, 2017]
   Fixed arm/aarch64 detection in CMakeLists.txt (Gianfranco Costamagna).
   Added option to Cmake build allowing a custom location of zlib to be
     specified in a scenario where libpng is being built as a subproject
@@ -33,7 +33,7 @@ Version 1.6.28beta01 [January 3, 2017]
   Changed png_ptr->options from a png_byte to png_uint_32, to accomodate
     up to 16 options.
 
-Version 1.6.28beta02 [January 4, 2017]
+Version 1.6.28rc02 [January 4, 2017]
   Added "include(GNUInstallDirs)" to CMakeLists.txt (Gianfranco Costamagna).
   Moved SSE2 optimization code into the main libpng source directory.
     Configure libpng with "configure --enable-intel-sse" or compile