Fix issue with 'sed' command on Mac OS X.
When running the script on Mac OS X, the sed command expects a parameter with the -i flag that specifies the backup extension. In this case, no backup is needed, so it can be a blank string.
Merge pull request #38 from caseyscarborough/patch-1

Fix issue with 'sed' command on Mac OS X.
Try preventing the race condition in PtyRecorder test