Hopefully fix travis ci

In the logs it says that `rake` specified in gemspec file doesn't match the one installed in travis.
Added notice about #281
exit with code only if it's Numeric > 0
SystemExit#status is Fixnum, so there's no need to check for Numeric
issue #305. prevent resultset loss by placing flock on separate lock file.
Fixed a few typos and grammatical errors in the readme.
Merge pull request #310 from npostolovski/typo_fixes_in_readme

Fixed a few typos and grammatical errors in the readme.
Merge pull request #309 from kdeberk/master

issue #305. prevent resultset loss by placing flock on separate lock file
Use bundle exec for travis.yml
fix build
Merge pull request #302 from hajder/master

Exit with code only if it's Numeric > 0
Merge pull request #278 from deivid-rodriguez/patch-1

Hopefully fix travis ci