Remove React warning

Fire onOptionChange in componentWillMount, otherwise end up trying
to update state effectively in a render method, which is bad.

src/components/views/login/CountryDropdown.js

@@ -43,8 +43,10 @@ export default class CountryDropdown extends React.Component {
         this.state = {
             searchQuery: '',
         }
+    }
 
-        if (!props.value) {
+    componentWillMount() {
+        if (!this.props.value) {
             // If no value is given, we start with the first
             // country selected, but our parent component
             // doesn't know this, therefore we do this.