Reduced output doesn't contain match string

[pwaller]

See #25.

Given this testcase:

https://gist.github.com/pwaller/a99e3836293e23677ad08052263b293a

If you run goreduce -match=StructOf ., goreduce deletes the x decl and exits.

The resulting file when run does not output the string StructOf anywhere, contrary to my expectation.