Fix broken markdown in docs (#306).

lib/src/rules/unnecessary_getters_setters.dart

Index: lib/src/rules/unnecessary_getters_setters.dart
diff --git a/lib/src/rules/unnecessary_getters_setters.dart b/lib/src/rules/unnecessary_getters_setters.dart
index bf79b722c1a17acfed284108fd5f312358834100..b0e76feeec84a233f73915bd985c5b939784e8d4 100644
--- a/lib/src/rules/unnecessary_getters_setters.dart
+++ b/lib/src/rules/unnecessary_getters_setters.dart
@@ -12,7 +12,7 @@ import 'package:linter/src/linter.dart';
 const desc = 'Avoid wrapping fields in getters and setters just to be "safe".';
 
 const details = '''
-From the [style guide] (https://www.dartlang.org/articles/style-guide/):
+From the [style guide](https://www.dartlang.org/articles/style-guide/):
 
 *AVOID** wrapping fields in getters and setters just to be "safe".