Update README.md

Use https link for installing

Will prevent : 

```
fatal: unable to connect to github.com:
github.com[0: 140.82.121.3]: errno=Connection timed out
```

README.md

@@ -94,7 +94,7 @@ troubleshoot and submit enhancements and fixes.
 
 Grab a copy of autojump:
 
-    git clone git://github.com/wting/autojump.git
+    git clone https://github.com/wting/autojump.git
 
 Run the installation script and follow on screen instructions.