Fix broken markdown in docs (#306).

lib/src/rules/one_member_abstracts.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.one_member_abstracts;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:linter/src/linter.dart';
 
 const desc =
     'Avoid defining a one-member abstract class when a simple function will do.';
 
 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** defining a one-member abstract class when a simple function will do.
 
 Unlike Java, Dart has first-class functions, closures, and a nice light syntax
 for using them. If all you need is something like a callback, just use a
 function. If you're defining an class and it only has a single abstract member
 with a meaningless name like `call` or `invoke`, there is a good chance
 you just want a function.
 
 **GOOD:**
@@ skipping 33 matching lines @@
       var member = node.members[0];
       if (member is MethodDeclaration &&
           member.isAbstract &&
           !member.isGetter &&
           !member.isSetter) {
         rule.reportLint(node.name);
       }
     }
   }
 }