Fix broken markdown in docs (#306).

lib/src/rules/one_member_abstracts.dart

Index: lib/src/rules/one_member_abstracts.dart
diff --git a/lib/src/rules/one_member_abstracts.dart b/lib/src/rules/one_member_abstracts.dart
index 9b8b4b18a7b24cb86fd744fd85680d659459a123..1b51728bea8c7724306eb76bfc2dc62afc5ba20c 100644
--- a/lib/src/rules/one_member_abstracts.dart
+++ b/lib/src/rules/one_member_abstracts.dart
@@ -12,7 +12,7 @@ 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.