Fix rails#724

This fixes an issue where, when the Spring client times out or otherwise
disconnects from the server, that the server crashes with a `Broken pipe
(Errno::EPIPE)` error.

Author: f1sherman

lib/spring/server.rb

@@ -74,6 +74,8 @@ def serve(client)
       end
     rescue SocketError => e
       raise e unless client.eof?
+    rescue Errno::EPIPE => e
+      log "client disconnected with error #{e.message}, ignoring command"
     ensure
       redirect_output
     end