Add build-matrix support

.travis.yml

@@ -1,13 +1,17 @@
 language: python
-python:
+sudo: false
-  - "3.3"
-  - "3.4"
-  - "3.5"
-  - "3.6"
-  - "3.7-dev"
-  - "3.8-dev"
-  - "pypy3.5"
-cache: pip
 install: "pip install -r requirements.txt"
 script: nosetests dnstraceroute.py
+matrix:
+    fast_finish: true
+    include:
+        - python: "3.3"
+        - python: "3.4"
+        - python: "3.5"
+        - python: "3.6"
+        - python: "3.7"
+        - python: "3.8-dev"
+        - python: "pypy3"
+          dist: xenial
+          sudo: true