Remove unused yaml import

.travis.yml

@@ -13,7 +13,6 @@ install:
   - pip install i3ipc
   - pip install psutil
   - pip install netifaces
-  - pip install pyyaml
   - pip install -U coverage==4.3
   - pip install codeclimate-test-reporter
   - pip install taskw

bumblebee/theme.py

@@ -6,7 +6,6 @@ import os
 import glob
 import copy
 import json
-import yaml
 import io
 import re
 import logging