Fix version-search pattern in rename_to_version.py

A while ago I made a misguided "improvement" to Version.h to use
constexpr instead of const. What could go wrong? Well, it turns out that
there were two separate references to the exact format of that line. The
upgrade-detection logic looked for 'const float kCurrentVersion' and so
did the .zip file renaming logic. The simplest code cleanups can break
things.

Author: randomascii

rename_to_version.py

@@ -1,7 +1,7 @@
 import os
 import sys
 
-prefix = 'constexpr float kCurrentVersion = '
+prefix = 'const float kCurrentVersion = '
 
 version_header = sys.argv[1]
 for line in open(version_header).readlines():