Fixed an error was being raised as pointed at insin#12 even if one fo…

…llow the docs:

    Warning: Failed propType: Required prop `form` was not specified in `BootstrapForm`. Check the render method of `App`.

As far as I see the `required` of form is only used in order to guarantee it is used between a newforms.Form tag. But if you don`t pass it, an error is raised anyway:
   Uncaught TypeError: Cannot read property `__patchedByBootstrapForm` of undefined

So I removed the mandatory form and made a validation inside render.

src/index.jsx

@@ -184,7 +184,6 @@ var BootstrapForm = React.createClass({
   },
 
   propTypes: {
-    form: React.PropTypes.instanceOf(Form).isRequired,
     spinner: React.PropTypes.string
   },
 
@@ -194,11 +193,17 @@ var BootstrapForm = React.createClass({
     }
   },
 
-  render() {
-    patchForm(this.props.form)
-    return <div>
-      {this.renderRows()}
-    </div>
+  render:function() {
+    if (this.props.form === undefined) {
+      console.error("Warning newforms-bootstrap requires to be passed between newforms.Form tags.");
+      return React.createElement("div", null, null);
+    }
+    else {
+      patchForm(this.props.form)
+      return React.createElement("div", null, 
+        this.renderRows()
+      )
+    }
   },
 
   renderRows() {