Fixed the method lookup for get_observation. Was failing on indexing …

…array using a string. The returned type is an array of dicts and needs searching to pull out the correct HTTP method URL

owslib/swe/observation/sos200.py

@@ -151,7 +151,10 @@ def get_observation(self, responseFormat=None,
             anything else e.g. vendor specific parameters
         """
 
-        base_url = self.get_operation_by_name('GetObservation').methods[method]['url']        
+        # Pluck out the get observation URL for HTTP method - methods is an
+        # array of dicts
+        methods = self.get_operation_by_name('GetObservation').methods
+        base_url = [ m['url'] for m in methods if m['type'] == method][0]
 
         request = {'service': 'SOS', 'version': self.version, 'request': 'GetObservation'}