feat: use the default configuration if none is specified (#33)

* It should work without configuration, just use default one

* It should warn user if .stylelintrc file does not exit

* Add warnings check

index.js

@@ -10,6 +10,7 @@ var formatter = require('stylelint/dist/formatters/stringFormatter').default;
 var runCompilation = require('./lib/run-compilation');
 
 function apply(options, compiler) {
+  options = options || {};
   var context = options.context || compiler.context;
 
   options = assign({

test/fixtures/test9/index.js

@@ -0,0 +1,3 @@
+require(getPath('./../../../node_modules/file-loader/index') + '!./test.scss');
+
+console.log('test9');

test/fixtures/test9/test.scss

@@ -0,0 +1,3 @@
+body {
+  display: block;
+}

test/index.js

@@ -90,4 +90,20 @@ describe('stylelint-webpack-plugin', function () {
         expect(stats.compilation.warnings).to.have.length(1);
       });
   });
+
+  it('works without StyleLintPlugin configuration but posts warnign .stylelintrc file not found', function () {
+    var config = {
+      context: './test/fixtures/test9',
+      entry: './index',
+      plugins: [
+        new StyleLintPlugin()
+      ]
+    };
+
+    return pack(assign({}, baseConfig, config))
+      .then(function (stats) {
+        expect(stats.compilation.errors).to.have.length(0);
+        expect(stats.compilation.warnings).to.have.length(0);
+      });
+  });
 });