Enabled support for multiple sln files

Fixed bug where each additional piped file would add to the list of parameters for the nuget restore call. Each file is now added to a local array instead of pushing to a global array.

index.js

@@ -27,8 +27,8 @@ module.exports = function (options) {
             cb(null, file);
             return;
         }
-        cmdArgs.push(file.path);
-        return execFile(targetFile, cmdArgs, function (error, stdout, stderror) {
+        var localArgs = cmdArgs.concat(file.path);
+        return execFile(targetFile, localArgs, function (error, stdout, stderror) {
             if (stdout.trim()) {
               gutil.log(stdout);
             }