Add option to invalidate cache when Gruntfile.js changes

[dmartin-gh]

When using grunt-jscs or grunt-contrib-jshint, editing your linting rules does not cause your entire source tree to be re-linted unless you run grunt clean or manually remove the .cache/ directory. This can lead to mistakenly thinking your source tree is compliant with the linting changes until you run a clean build at a later time.

It would be nice if there was an option to grunt-newer to tell it to invalidate the entire .cache/ directory if Gruntfile.js has been modified since the last run. Finding a solution that also works with load-grunt-config could be tricky.

If you're not using load-grunt-config, a workaround is (Unix only):

/** Clear grunt-newer cache when gruntfile.js changes */
function maybeClearNewerCache(grunt) {
    var lastRunTime;
    try {
        lastRunTime = fs.statSync('.grunt-record').mtime;
    } catch (e) {
        lastRunTime = new Date(0);
    }   

    if (fs.statSync(__filename).mtime > lastRunTime) {
        var cmd = { cmd: 'rm', args: ['-rf', './node_modules/grunt-newer/.cache'] };
        grunt.util.spawn(cmd, function (error, result, code) {
            if (error) { grunt.fatal(error); }
        }); 
    }   
}

maybeClearNewerCache(grunt);
grunt.registerTask('record', 'Record the build time', function () {
    grunt.file.write('.grunt-record', 'blah');
});
grunt.registerTask('default', [
    ... // other tasks here
    'record'
]);

[shospodarets]

It's not only Gruntfile.js
There are plenty options:
.eslintrc
.jshintrc
and others.
So the best if there would be an options to define that for particular task on changing some files cache must be cleaned.
E.g.:

newer: {
 options: {
  ...
  revalidate: {
   "eslint": ['.eslintrc', '.eslintignore'],
   "jshint": ['.jshintrc', '.jshintignore']
  }
 }
}

[shospodarets]

These 2 issues are similar:
#83
#32