Lowercase repo name for consistency. Refs #251.

The repo name is sometimes refered as Copilot and other times as copilot
(in lowercase).

Using different cases for the same resource or element makes it harder
to find expressions in the repo using standard tools.

This commit simply updates the repo URL in the main cabal file and in
the README to consistently use lowercase for the repo name.

[ci skip]

Author: ivanperez-keera

copilot/README.md

@@ -76,7 +76,7 @@ have trouble building/installing.
 ## Example
 Here follows a simple example of a heating system. Other examples can be found
 in the [examples
-directory](https://github.com/Copilot-Language/Copilot/tree/master/examples)
+directory](https://github.com/Copilot-Language/copilot/tree/master/examples)
 of the main repository.
 
 ```haskell

copilot/copilot.cabal

@@ -30,7 +30,7 @@ extra-source-files:
 
 source-repository head
     type:       git
-    location:   https://github.com/Copilot-Language/Copilot.git
+    location:   https://github.com/Copilot-Language/copilot.git
 
 flag examples
     description: Enable examples