[ermine] Fix parsing double from string exception.

An exception is thrown when parsing json weather data for temp. It
is expecting a double and sometimes weather data comes back with
string value.

Change-Id: Ie2c1557f9fe011650e969da9cd677734f8916693
diff --git a/session_shells/ermine/settings/lib/src/weather.dart b/session_shells/ermine/settings/lib/src/weather.dart
index 28bf1ac..509f8ae 100644
--- a/session_shells/ermine/settings/lib/src/weather.dart
+++ b/session_shells/ermine/settings/lib/src/weather.dart
@@ -107,7 +107,7 @@
         properties['temperature']['value'] != null) {
       location
         ..observation = properties['textDescription']
-        ..tempInDegrees = properties['temperature']['value'].toDouble();
+        ..tempInDegrees = double.parse(properties['temperature']['value']);
     }
   }