Travis: add a tor 0.3.5 and a tor nightly build

.travis.yml

@@ -18,12 +18,30 @@ os:
 #    -
 
 matrix:
+  # include creates Linux, python 2.7, tor stable builds by default
   include:
     ## Test macOS with its default python version, and work around an issue
     ## with language: python on Travis macOS
     - os: osx
       language: c
-    ## Test Linux against all supported python releases
+    ## Test tor 0.3.5 and tor nightly
+    - addons:
+        apt:
+          sources:
+            - sourceline: 'deb https://deb.torproject.org/torproject.org trusty main'
+              key_url: 'http://ha.pool.sks-keyservers.net/pks/lookup?search=0xA3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89&options=mr&op=get'
+            - sourceline: 'deb https://deb.torproject.org/torproject.org tor-experimental-0.3.5.x-trusty main'
+          packages:
+            - tor
+    - addons:
+        apt:
+          sources:
+            - sourceline: 'deb https://deb.torproject.org/torproject.org trusty main'
+              key_url: 'http://ha.pool.sks-keyservers.net/pks/lookup?search=0xA3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89&options=mr&op=get'
+            - sourceline: 'deb https://deb.torproject.org/torproject.org tor-nightly-master-trusty main'
+          packages:
+            - tor
+    ## Test all supported python releases
     - python: "2.7"
     - python: "3.4"
     - python: "3.5"