additionally check to make sure system is "Linux"

jeremylow · jeremylow · commit 5884ece2b7b2 · 2016-08-04T21:45:27.000-04:00
diff --git a/Makefile b/Makefile
@@ -1,9 +1,11 @@
 
 ifeq ($(shell uname -m),x86_64)
+ifeq ($(shell uname -s),Linux)
 PYPY53 = pypy-5.3-src
 else
 PYPY53 = pypy-5.3
 endif
+endif
 
 help:
 	@echo "  env         install all production dependencies"
