Bug fix: Removed incorrect escaping of single quotes.

[uncommoncode]

The JSON spec requires double quotes for keys. This would cause issues with other standard compliant parsers. The list of valid characters after an escape code is "\/bfnrtu (see http://json.org/ for more):

A simple way to reproduce:

In lua:

require("json")
json.save("example.json", {["'"] = 0})

In the command line:

python -mjson.tool < example.json

Output:

Invalid \escape: line 1 column 3 (char 2)

This fix removes escaping for the single quote, which is not part of the JSON spec.