fix typo in keras/layers/merge-> concatenate description
@@ -309,7 +309,7 @@ class Concatenate(_Merge):
"""Layer that concatenates a list of inputs.
It takes as input a list of tensors,
- all of the same shape expect for the concatenation axis,
+ all of the same shape except for the concatenation axis,
and returns a single tensor, the concatenation of all inputs.
# Arguments
