[gulp-less] Update the definition of IOptions

Add "modifyVars"
Make "paths" optional

gulp-less/gulp-less-tests.ts

@@ -4,6 +4,22 @@
 import gulp = require("gulp");
 import less = require("gulp-less");
 
+// Without options
+gulp.task("less", () => {
+    gulp.src("less/**/*.less")
+        .pipe(less())
+        .pipe(gulp.dest("public/css"));
+});
+
+// With an empty option object
+gulp.task("less", () => {
+    gulp.src("less/**/*.less")
+        .pipe(less({}))
+        .pipe(gulp.dest("public/css"));
+});
+
+
+// With some options
 gulp.task("less", () => {
     gulp.src("less/**/*.less")
         .pipe(less({

gulp-less/gulp-less.d.ts

@@ -8,7 +8,8 @@
 declare module "gulp-less" {
 
     interface IOptions {
-        paths: string[];
+        modifyVars?: {};
+        paths?: string[];
         plugins?: any[];
     }