Correction of a double negation

The sentence seemed to imply that return codes from modules are significant, while they are not. The second part of the sentence confirms this, as it advises to use standard return codes only for future proofing.

docsite/rst/developing_modules.rst

@@ -347,7 +347,7 @@ and guidelines:
 
 * In the event of failure, a key of 'failed' should be included, along with a string explanation in 'msg'.  Modules that raise tracebacks (stacktraces) are generally considered 'poor' modules, though Ansible can deal with these returns and will automatically convert anything unparseable into a failed result.  If you are using the AnsibleModule common Python code, the 'failed' element will be included for you automatically when you call 'fail_json'.
 
-* Return codes from modules are not actually not significant, but continue on with 0=success and non-zero=failure for reasons of future proofing.
+* Return codes from modules are actually not significant, but continue on with 0=success and non-zero=failure for reasons of future proofing.
 
 * As results from many hosts will be aggregated at once, modules should return only relevant output.  Returning the entire contents of a log file is generally bad form.