Renamed FormBuilderValidators.IP to FormBuilderValidators.ip to follow naming conventions

Author: danvick

lib/src/form_builder_validators.dart

@@ -208,7 +208,7 @@ class FormBuilderValidators {
 
   /// [FormFieldValidator] that requires the field's value to be a valid IP address.
   /// * [version] is a `String` or an `int`.
-  static FormFieldValidator<String> IP(
+  static FormFieldValidator<String> ip(
     BuildContext context, {
     dynamic version,
     String errorText,

test/form_builder_validators_test.dart

@@ -289,7 +289,7 @@ void main() {
   testWidgets(
       'FormBuilderValidators.IP',
       (WidgetTester tester) => testValidations(tester, (context) {
-            final validator = FormBuilderValidators.IP(context);
+            final validator = FormBuilderValidators.ip(context);
             // Pass
             expect(validator(null), isNull);
             expect(validator(''), isNull);