Allow pipe ('|') in Graphite lexer

Allow for Graphite lexer to understand metric names like
'net|usage_average'.

public/app/plugins/datasource/graphite/lexer.js

@@ -120,6 +120,7 @@ define([
       i >= 48 && i <= 57 || // 0-9
       i === 36 ||           // $
       i === 126 ||          // ~
+      i === 124 ||          // |
       i >= 65 && i <= 90 || // A-Z
       i === 95 ||           // _
       i === 45 ||           // -