fix doc.

paddle/operators/unpool_op.cc

@@ -53,15 +53,14 @@ class Unpool2dOpMaker : public framework::OpProtoAndCheckerMaker {
         "(string), unpooling type, can be \"max\" for max-unpooling ")
         .InEnum({"max"});
     AddComment(R"DOC(
-        "Input shape: $(N, C_{in}, H_{in}, W_{in})$
+"Input shape: $(N, C_{in}, H_{in}, W_{in})$, 
 Output shape: $(N, C_{out}, H_{out}, W_{out})$
 Where
 $$
 H_{out} = (H_{in}−1) * strides[0] − 2 * paddings[0] + ksize[0] \\
 W_{out} = (W_{in}−1) * strides[1] − 2 * paddings[1] + ksize[1]
 $$
-        Paper: http://www.matthewzeiler.com/wp-content/uploads/2017
-        /07/iccv2011.pdf
+Paper: http://www.matthewzeiler.com/wp-content/uploads/2017/07/iccv2011.pdf
 )DOC");
   }
 };