Fixes a crash of casting bytes to Python string

The crash happened when cuDNN isn't used and the error message was raised. However, the message was a 'bytes' object, not a string. Casting the bytes to string solves the issue.

Fixes a crash of casting bytes to Python string
d1e6d0e5 · ASalvail · b6410099 · d1e6d0e5
--- a/theano/sandbox/cuda/dnn.py
+++ b/theano/sandbox/cuda/dnn.py
@@ -56,7 +56,7 @@ if ((err = cudnnCreate(&_handle)) != CUDNN_STATUS_SUCCESS) {
            else:
                dnn_available.msg = (
                    "Theano is not able to use cuDNN. We got this error: \n" +
-                    err)
+                    str(err))
    return dnn_available.avail