Use regex for carriage return in windows

In windows env, the ImageMagick version string is containing `\r\n` at the end
of each line, split and replace methods are keeping this `\r` leading to
an issue with `semver.valid()` returning `false` because extracted `imVersion`
is something like `"6.9.3-2\r"`.

Closes gh-12

Author: laurentgoncalves

lib/themeroller-image.js

@@ -348,7 +348,7 @@ async.series( [
 			if ( !( /ImageMagick/ ).test( output ) ) {
 				return callback( new Error( "ImageMagick not installed.\n" + output ) );
 			}
-			imVersion = output.split( "\n" )[ 0 ].replace( /^Version: ImageMagick ([^ ]*).*/, "$1" );
+			imVersion = output.split( /\r?\n/ )[ 0 ].replace( /^Version: ImageMagick ([^ ]*).*/, "$1" );
 			if ( !semver.valid( imVersion ) ) {
 				return callback( new Error( "Could not identify ImageMagick version.\n" + output ) );
 			}