Add Python 3.7 to Travis and update to go-IPFS v0.4.18

.travis.yml

@@ -1,4 +1,7 @@
 language: python
+# Testing Python 3.7 requires using the `xenial` dist which uses
+# virtual machines rather than LXC and tends to take longer, so
+# use it only where necessary
 matrix:
   include:
   - python: "2.7"
@@ -9,17 +12,20 @@ matrix:
     env: TOXENV=py35
   - python: "3.6"
     env: TOXENV=py36
+  - python: "3.7"
+    env: TOXENV=py37
+    dist: xenial
   - python: "3.6"
     env: TOXENV=codestyle
     before_install: true
 
 before_install:
-  - wget "https://dist.ipfs.io/go-ipfs/v0.4.14/go-ipfs_v0.4.14_linux-amd64.tar.gz" -O /tmp/ipfs.tar.gz
+  - wget "https://dist.ipfs.io/go-ipfs/v0.4.18/go-ipfs_v0.4.18_linux-amd64.tar.gz" -O /tmp/ipfs.tar.gz
   - mkdir -p $HOME/bin
   - pushd . && cd $HOME/bin && tar -xzvf /tmp/ipfs.tar.gz && popd
   - export PATH="$HOME/bin/go-ipfs:$PATH"
 
 install:
   - pip install tox
 
-script: tox
+script: tox

tox.ini

@@ -4,7 +4,8 @@ envlist =
 	py27,
 	py34,
 	py35,
-	py36
+	py36,
+	py37
 
 # Tox' sdist feature presumes that `./setup.py sdist` is available
 # Disable this feature until PEP-517 is implemented by both tox and flit.