Update to latest level-ttl

An older version of level-ttl was causing level-session
    to leak timers.

```
timer handle (`setTimeout(wrapper, 10000)`)
timer handle leaked at one of: 
    at /home/raynos/projects/manga-feed/node_modules/level-session/node_modules/level-ttl/level-ttl.js:8:28
timer listener function wrapper() {
```

I couldn't run my tests cleanly because level-ttl would
    allocate a timer and caused my tests to hang. i.e.
    `levelSession.close()` doesnt actually close it.

This bug was fixed in level-ttl in 0.6.0.

This PR:

 - fixes your tests by dealing with a `request` breaking
    change.
 - updates your dev dependencies to be ranges (not *)
 - updates level-ttl to the latest version.

This is a backwards incompatible breaking change. Any
    sessions stored with the older version of ttl will
    not expire properly since level-ttl uses a different
    keyspace to store its information under.

Recommended version change: **major**.

cc @rvagg