Fix invalide use of encode on bytes object

Within the pywps.inout.inputs.ComplexInput the json convertion function
use encode where decode should be used. The patch fix this issue.

pywps/inout/inputs.py

@@ -247,7 +247,7 @@ def _json_data(self, data):
                 else:
                     # Otherwise we assume all other formats are unsafe and need to be enclosed in a CDATA tag.
                     if isinstance(self.data, bytes):
-                        out = self.data.encode(self.data_format.encoding or 'utf-8')
+                        out = self.data.decode(self.data_format.encoding or 'utf-8')
                     else:
                         out = self.data