Adding units as a valid options

Author: dNitza

README.md

@@ -25,6 +25,9 @@ Add the following to your **Gemfile**
     # get current weather by geocode. (lat, lon)
     OpenWeather::Current.geocode(9.94, 76.26)
 
+    # get the current weather in degrees celsius
+    OpenWeather::Current.city("Cochin, IN", units: 'metric')
+
     # weather forecast APIs
 
     # get weather forecast by city name

lib/open_weather/base.rb

@@ -24,7 +24,7 @@ def success?
     private
 
     def extract_options!(options)
-      valid_options = [:lat, :lon, :city, :country, :id]
+      valid_options = [:lat, :lon, :city, :country, :id, :units]
       options.keys.each { |k| options.delete(k) unless valid_options.include?(k) }
 
       if options[:city] || options[:country]