Minor fix for code block.
Minor fix for code block.

cherryc/dynet,kamigaito/cnn,Peilun-Li/dynet,cherryc/dynet,Peilun-Li/dynet,mitchellstern/dynet,Abasyoni/dynet,Peilun-Li/dynet,kamigaito/cnn,mitchellstern/dynet,Abasyoni/dynet,Abasyoni/dynet,cherryc/dynet