Use https for tests submodule so that non-developers can clone easily

Author: ben-brewer-codethink

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "tests"]
 	path = tests
-	url = git@github.com:CodethinkLabs/ofc-tests.git
+	url = https://github.com/CodethinkLabs/ofc-tests.git

.travis.yml

@@ -6,8 +6,6 @@ git:
     # If you use a depth of 1 and have a queue of jobs, Travis CI won’t build
     # commits that are in the queue when you push a new commit.
     depth: 3
-    # Handle submodules manually to avoid permission problems.
-    submodules: false
 
 # whitelist
 branches:
@@ -28,10 +26,5 @@ addons:
 compiler:
     - gcc-4.8
 
-before_install:
-    # Replace the SSH URL with the public URL and initialize submodules
-    - sed -i 's/[email protected]:/https:\/\/github.com\//' .gitmodules
-    - git submodule update --init --recursive
-
 script:
     - make -j 2 test