Add support for -moz-osx vendor prefix

Since Firefox 25 the vendor prefix `-moz-osx` is supported:
https://bugzilla.mozilla.org/show_bug.cgi?id=857142#c83

Add support for this vendor prefix to the `PropertySortOrder` linter.

Change-Id: Ib5b328bad6d2403dfe5fdf05debf188f0225282b
Reviewed-on: http://gerrit.causes.com/36110
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Update Sass dependency from 3.3.0.rc.1 -> 3.3.0

Sass 3.3.0 has finally been released, so update our dependency to use
that version. We can't support anything before this version going
forward due to the monkey-patching we employ and the fact that we are
highly dependent on the new source map support included in 3.3.0.

In order to get the specs to pass, the following changes were made:

 * Class methods `node_name` and `visit_method` were dynamically defined
   for all Sass::Script::Value and Sass::Script::Tree types

 * `SpaceAfterComma` linter had its `check_commas_after_args`
   implementation changed to scan outwards from the end of the source
   range to find the comma (since the Sass parser was unpredictable in
   where it would consider the end of the source range)

 * `ZeroUnit` linter implementation was changed to check the original
   source for units, since the parser now seems to strip units when the
   value is zero

Closes #81, #89

Change-Id: I8b9c02a6de36d92ba6be0d3d0f509192da64334a
Reviewed-on: http://gerrit.causes.com/36133
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Fix source_from_range for single lines

The `source_from_range` helper was incorrect since it returned the
entire line for single-line ranges, even if the end position was not the
end of the line.

In the process, this revealed two specs that were incorrectly coded.
They previously assumed that a lint could be reported for strings with
interpolation. We actually can't check if a string with interpolation
will have characters that justify single or double quotes (for example,
the string "hello #{"'" + 'world' + "'"}" should not report a lint, but
with the specs as written this would be expected to report a lint).

Change the behavior to fix this bug.

Change-Id: I1432ea1e423421ee5e882bfd10ab7a677347bcbb
Reviewed-on: http://gerrit.causes.com/36134
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Add basic Rubocop configuration

Copied from the Overcommit repository.

Change-Id: I9f3129e0d2cd95d2d7cbb4fdc9b67af5e8d4ff73
Reviewed-on: http://gerrit.causes.com/36135
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Gracefully handle invalid configuration files

Previously, `scss-lint` would raise "Report this bug" error when reading
an invalid configuration file. This isn't really a problem with
`scss-lint`, but the configuration file, so it should be more gracefully
handled.

Add support for reporting a nicer error message when invalid
configurations are provided.

Fixes #85

Change-Id: Ic4afe64a17fa24a04682003cd12d649efd54a261
Reviewed-on: http://gerrit.causes.com/36136
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Cut version 0.19.0

Change-Id: I7a69e3dcd0f1f2533024f2e04c5d11475751b163
Reviewed-on: http://gerrit.causes.com/36137
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Add Sass 3.3.0 dependency to README

We get a question every once in a while about `scss-lint` not working
for an older version of Sass. Hopefully explicitly mentioning this will
reduce the number of inquiries.

Change-Id: Ic761ddec1183ecab1da5b70fbe7dc1a0cbd9a4bf
Reviewed-on: http://gerrit.causes.com/36179
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>