Python compat - no explicit reference to Python version

Update documentation and shebang.

Differential Revision: https://reviews.llvm.org/D56252

llvm-svn: 350327
diff --git a/llvm/utils/update_llc_test_checks.py b/llvm/utils/update_llc_test_checks.py
index d85fed5..960fee2 100755
--- a/llvm/utils/update_llc_test_checks.py
+++ b/llvm/utils/update_llc_test_checks.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python
 
 """A test case update script.