[docs] use angle brackets in MAINTAINER example email

docs/sources/use/builder.rst

@@ -321,7 +321,7 @@ the command given by ``CMD`` is executed.
     # VERSION               0.0.1
 
     FROM      ubuntu
-    MAINTAINER Guillaume J. Charmes "guillaume@dotcloud.com"
+    MAINTAINER Guillaume J. Charmes <guillaume@dotcloud.com>
 
     # make sure the package repository is up to date
     RUN echo "deb http://archive.ubuntu.com/ubuntu precise main universe" > /etc/apt/sources.list