Fix escape in commit_id calculation

Author: brson

master/master.cfg

@@ -1324,7 +1324,7 @@ def packaging_dist_buildfactory(platform, channel_label):
     # Routing stderr to /dev/null is to work around a
     # mysterious bug on windows where cat thinks I'm trying to pipe
     # file called '^'.
-    source_id = "cat tmp/work/rustc-*/version 2> /dev/null | sed 's/^.*(\([a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9]\).*/\1/'"
+    source_id = 'cat tmp/work/rustc-*/version 2> /dev/null | sed "s/^.*(\([a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9]\).*/\\1/"'
     f.addStep(SetPropertyFromCommand(env=CommandEnv(),
                                      command=["sh", "-c", source_id],
                                      property="commit_id",