Disable auto capitalization for login field

This is either an email or a phone number. Phone numbers aren't
capitalized, and emails are not typically capitalized. Disabling
auto-capitalization ("sentence" is the default) should make this field
more convenient for most users

src/page/SignInPage.js

@@ -93,6 +93,7 @@ class App extends Component {
                                 textContentType="username"
                                 onChangeText={text => this.setState({login: text})}
                                 onSubmitEditing={this.submitForm}
+                                autoCapitalize="none"
                             />
                         </View>
                         <View style={[styles.mb4]}>