Update Yahoo lookup to reflect API changes.

"Results" key is now "Result" and is not an array when only one result.

lib/geocoder/lookups/yahoo.rb

@@ -13,7 +13,7 @@ module Geocoder::Lookup
     def results(query)
       return [] unless doc = fetch_data(query)
       if doc = doc['ResultSet'] and doc['Error'] == 0
-        return doc['Found'] > 0 ? doc['Results'] : []
+        return doc['Found'] > 0 ? Array(doc['Result']) : []
       else
         warn "Yahoo Geocoding API error: #{doc['Error']} (#{doc['ErrorMessage']})."
         return []

test/fixtures/yahoo_garbage.json

@@ -6,7 +6,7 @@
     "Locale":"us_US",
     "Quality":87,
     "Found":1,
-    "Results":[{
+    "Result":[{
       "quality":9,
       "latitude":"55.008390",
       "longitude":"-5.822485",

test/fixtures/yahoo_madison_square_garden.json

@@ -6,7 +6,7 @@
     "Locale":"us_US",
     "Quality":90,
     "Found":1,
-    "Results":[{
+    "Result":[{
       "quality":90,
       "latitude":"40.750381",
       "longitude":"-73.993988",