solc version check should be exact

[ewingrj]

Currently the solc version checks that the installed version is > the requested version. However it should check for an exact match. When I specify a solc version in embark.json, I expect the contracts to be compiled with that version.

Current behavior when using this plugin...

If solc is available via solc cmd, & solc version > embark.json solc version, use that.
else, use solcjs with specified solc version from embark.json.

Thus leading to different end results for different repo installations