Fixing issue #12 correct handling of format argument

[craigedmunds]

I don't think the defaulting of format to json is necessary at all? Although the absence of tests makes it difficult to gauge!

[farmerpaul]

I agree, not sure what the rationale is behind those original lines of code (if the format parameter already exists, then change it to json, but then if it doesn't exist, don't do anything?). I had to use your fork in my project to make any progress in using the search_replace command, thanks for posting it.