Fix missing reference to pypy_architecture

plugins/python-build/share/python-build/pyston-0.5.1

@@ -11,7 +11,7 @@ case "$(pyston_architecture 2>/dev/null || true)" in
 * )
   { echo
     colorize 1 "ERROR"
-    echo ": A Pyston 0.5.1 binary is not available for $(pypy_architecture 2>/dev/null || true)."
+    echo ": A Pyston 0.5.1 binary is not available for $(pyston_architecture 2>/dev/null || true)."
     echo
   } >&2
   exit 1