Fix typos in Catalan (darkskyapp#208)

* Typo

In Catalan, we generally write J before A, O, or U, and G before E, or I. The rule applies in this case.

* Removed capitalization of days of the week

In Catalan, the days of the week are only capitalized if they are the first word of a sentence.

lib/lang/ca.js

@@ -29,7 +29,7 @@ module.exports = {
   "possible-light-rain": "possible plugim",
   "light-rain": "pluja lleugera",
   "medium-rain": "pluja",
-  "heavy-rain": "plujes fortes",
+  "heavy-rain": "pluges fortes",
   "possible-very-light-sleet": "possible aiguaneu",
   "very-light-sleet": "aiguaneu",
   "possible-light-sleet": "possible aiguaneu",
@@ -71,13 +71,13 @@ module.exports = {
   "night": "a la nit",
   "today": "avui",
   "tomorrow": "demà",
-  "sunday": "el Diumenge",
-  "monday": "el Dilluns",
-  "tuesday": "el Dimarts",
-  "wednesday": "el Dimecres",
-  "thursday": "el Dijous",
-  "friday": "el Divendres",
-  "saturday": "el Dissabte",
+  "sunday": "el diumenge",
+  "monday": "el dilluns",
+  "tuesday": "el dimarts",
+  "wednesday": "el dimecres",
+  "thursday": "el dijous",
+  "friday": "el divendres",
+  "saturday": "el dissabte",
   "next-sunday": "el pròxim diumenge",
   "next-monday": "el pròxim dilluns",
   "next-tuesday": "el pròxim dimarts",