fix url and checksum for pypy-2.5.1-src

plugins/python-build/share/python-build/pypy-2.5.1-src

@@ -1,2 +1,2 @@
 require_gcc
-install_package "pypy-pypy-9c4588d731b7" "https://bitbucket.org/pypy/pypy/get/release-2.5.1.tar.bz2#58cefb30a645f7b535e2b63a1d7c21bf12615ad95324bc6c919df90f7b2f37ef" "pypy_builder" verify_py27 ensurepip
+install_package "pypy-2.5.1-src" "https://bitbucket.org/pypy/pypy/downloads/pypy-2.5.1-src.tar.bz2#ddb3a580b1ee99c5a699172d74be91c36dda9a38946d4731d8c6a63120a3ba2a" "pypy_builder" verify_py27 ensurepip