[fixed] server side rendering for Modal component

Using document reference in the render method will throw an error
on React.renderToString call on the server side.
See react-bootstrap#717.

The proper solution is to remove document.querySelector check. Obviously
we cant detect this feature on the server side, besides it leads to
differencies btw server and client side rendering output, so React will warn
about it, ex:

1. `render` on the server side will apply classes: `modal fade`
2. `render` on the client side will apply clasess: `modal fade in`

Also karma test environment is not suitable for testing server side rendering,
so mocha test run againt nodejs was added.

Author: maxmalov

Diff for: package.json

@@ -10,7 +10,7 @@
   "scripts": {
     "build": "babel-node tools/build-cli.js",
     "test-watch": "karma start",
-    "test": "npm run lint && npm run build && karma start --single-run",
+    "test": "npm run lint && npm run build && karma start --single-run && _mocha --compilers js:babel-core/register './test/server/*Spec.js'",
     "lint": "eslint ./",
     "docs-build": "babel-node tools/build-cli.js --docs-only",
     "docs": "docs/dev-run",

Diff for: src/Modal.js

@@ -43,7 +43,7 @@ const Modal = React.createClass({
     let classes = {
       modal: true,
       fade: this.props.animation,
-      'in': !this.props.animation || !document.querySelectorAll
+      'in': !this.props.animation
     };
 
     let modal = (
@@ -72,11 +72,10 @@ const Modal = React.createClass({
   renderBackdrop(modal) {
     let classes = {
       'modal-backdrop': true,
-      'fade': this.props.animation
+      fade: this.props.animation,
+      'in': !this.props.animation
     };
 
-    classes.in = !this.props.animation || !document.querySelectorAll;
-
     let onClick = this.props.backdrop === true ?
       this.handleBackdropClick : null;
 

Diff for: test/server/ModalSpec.js

@@ -0,0 +1,17 @@
+import React from 'react';
+import {assert} from 'chai';
+import Modal from '../../src/Modal.js';
+
+describe('Modal', () => {
+  it('Should be rendered on the server side', function () {
+    let noOp = () => {};
+
+    assert.doesNotThrow(function renderOnServerSide() {
+      return React.renderToString(
+        <Modal onRequestHide={noOp}>
+          <strong>Message</strong>
+        </Modal>
+      );
+    });
+  });
+});