Fix method syntax in ReadMe example code (#55)

The method was declared with an expression body but it ended with a `}`
diff --git a/README.md b/README.md
index 9d37e21..c0c12ad 100644
--- a/README.md
+++ b/README.md
@@ -104,7 +104,7 @@
 }
 
 // Using CharacterRange operations.
-Characters firstTagCharacters(Characters source) =>
+Characters firstTagCharacters(Characters source) {
   var range = source.findFirst("<".characters);
   if (range != null && range.moveUntil(">".characters)) {
     return range.currentCharacters;