ndk-gdb.cmd: point to the right place.

ndk-gdb is not ndk-gdb.py.

Bug: https://github.com/android-ndk/ndk/issues/46
Change-Id: I0d2ce002f2526b0ce80e55540e45903dbb77c147

ndk-gdb.cmd

@@ -2,5 +2,5 @@
 setlocal
 set PREBUILT_BIN=%~dp0
 set SHELL=cmd
-"%PREBUILT_BIN%/python.exe" -u "%~dp0ndk-gdb" %*
+"%PREBUILT_BIN%/python.exe" -u "%~dp0ndk-gdb.py" %*
 endlocal