Fix coffelint error causing Travis builds to fail

Currently, running coffeelint produces this error and causes Travis
builds to fail:

```
Running "coffeelint:src" (coffeelint) task
src/command-installer.coffee
  ✖  line 73  Line contains inconsistent indentation  Expected 2 got 0
✖ 1 error
Warning: Task "coffeelint:src" failed. Use --force to continue.
Error: Task "coffeelint:src" failed.
```

See https://github.com/clutchski/coffeelint/issues/189 for more information
on this problem and suggested approach, and for a different place in Atom
where this approach is used see this:

ca39c106d6/src/config.coffee (L984)

src/command-installer.coffee

@@ -71,5 +71,6 @@ module.exports =
             error = null
             symlinkCommandWithPrivilegeSync(commandPath, destinationPath)
           catch error
+            undefined
 
         callback?(error)