added configuration file path argument and fixed an error with invoke tasks

[tylerlaberge]

Following the contribution guidelines, the 'invoke install' command would cause an error until I added a 'context' positional argument to each of the tasks. The issue and fix is discussed more at pyinvoke/invoke#362.

I also added a configuration file path argument to the jasmine command in order to allow users to specify a desired path rather than being forced to use 'spec/javascripts/support/jasmine.yml' as the path. As it is now you simply can do 'jasmine --config 'some_path_to_configuration_file' and jasmine will now use that configuration file.

[sgravrock]

Thanks for your contribution. We went in a different direction and removed invoke entirely (210060c and bf1a361). Invoke wasn't doing much for us, and keeping it as an un-versioned dependency would have left us open to more bugs like the one your PR was meant to fix.