Fix broken CI

.travis.yml

@@ -1,5 +1,9 @@
 language: python
 
+env:
+  global:
+    PIP_PREFER_BINARY=true # https://github.com/numba/llvmlite/issues/471
+
 python:
   - "2.7"
 #  - "3.3" # failed due to setuptool version
@@ -8,14 +12,14 @@ python:
   - "3.5-dev"  # 3.5 development branch
   - "3.6"
   - "3.6-dev"  # 3.6 development branch
-  
+
 install:
   - pip install --upgrade pip
   - pip install -r requirements_ci.txt
   - pip install pytest
   - pip install pytest-cov
   - pip install coveralls
-  
+
 # command to run tests
 script:
    pytest --cov=pyod/
@@ -28,4 +32,4 @@ notifications:
     recipients:
       - yzhao062@gmail.com
   on_success: never # default: change
-  on_failure: always # default: always
+  on_failure: always # default: always