Switch to Poetry for package management

.travis.yml

@@ -14,12 +14,19 @@ python:
 
 jobs:
   include:
-    - python: 3.7
-      name: "Check"
+    - stage: Checks
+      name: Check
       script: scripts/check
+    - name: Build
+      script: scripts/build
 
-script:
-  - scripts/test
+before_install:
+  - pip install --pre poetry
+
+install:
+  - poetry install -v
+
+script: scripts/test
 
 after_script:
   - if [ -f .coverage ]; then