Fix broken markdown in docs (#306).

lib/src/rules/unnecessary_getters_setters.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library linter.src.rules.unnecessary_getters_setters;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:linter/src/ast.dart';
 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".
 
 In Java and C#, it's common to hide all fields behind getters and setters
 (or properties in C#), even if the implementation just forwards to the field.
 That way, if you ever need to do more work in those members, you can without
 needing to touch the callsites. This is because calling a getter method is
 different than accessing a field in Java, and accessing a property isn't
 binary-compatible with accessing a raw field in C#.
 
@@ skipping 61 matching lines @@
   _visitGetterSetter(MethodDeclaration getter, MethodDeclaration setter) {
     if (isSimpleSetter(setter) &&
         isSimpleGetter(getter) &&
         !isProtected(getter) &&
         !isProtected(setter)) {
       rule.reportLint(getter.name);
       rule.reportLint(setter.name);
     }
   }
 }