Updated test requirements, added test37 and test38 commands

pi.yaml

@@ -1,12 +1,30 @@
 - !Image
   name: env36
-  from: !DockerImage python:3.6-slim
+  from: !DockerImage python:3.6.0-slim
   repository: localhost/grpclib/env36
   tasks:
   - run: pip3 install --no-cache-dir h2==3.1.0
   - run: pip3 install --no-cache-dir -r {{reqs}}
     reqs: !File "requirements.txt"
 
+- !Image
+  name: env37
+  from: !DockerImage python:3.7.0-slim
+  repository: localhost/grpclib/env37
+  tasks:
+  - run: pip3 install --no-cache-dir h2==3.1.0
+  - run: pip3 install --no-cache-dir -r {{reqs}}
+    reqs: !File "requirements.txt"
+
+- !Image
+  name: env38
+  from: !DockerImage python:3.8.0a4-slim
+  repository: localhost/grpclib/env38
+  tasks:
+  - run: pip3 install --no-cache-dir h2==3.1.0
+  - run: pip3 install --no-cache-dir -r {{reqs}}
+    reqs: !File "requirements.txt"
+
 - !Image
   name: docs
   from: env36
@@ -46,3 +64,17 @@
   run: py.test
   environ:
     PYTHONPATH: .
+
+- !Command
+  name: test37
+  image: env37
+  run: py.test
+  environ:
+    PYTHONPATH: .
+
+- !Command
+  name: test38
+  image: env38
+  run: py.test
+  environ:
+    PYTHONPATH: .

requirements.txt

@@ -2,21 +2,22 @@
 # This file is autogenerated by pip-compile
 # To update, run:
 #
-#    pip-compile -U --output-file requirements.txt requirements.in
+#    pip-compile --output-file=requirements.txt requirements.in
 #
 async-timeout==2.0.1
 atomicwrites==1.3.0       # via pytest
 attrs==19.1.0             # via pytest
 coverage==4.5.3           # via pytest-cov
-faker==1.0.5
+faker==1.0.7
 more-itertools==7.0.0     # via pytest
 multidict==4.5.2
-pluggy==0.9.0             # via pytest
+pluggy==0.11.0            # via pytest
 protobuf==3.7.1
 py==1.8.0                 # via pytest
 pytest-asyncio==0.10.0
-pytest-cov==2.6.1
-pytest==4.4.1
+pytest-cov==2.7.1
+pytest==4.5.0
 python-dateutil==2.8.0    # via faker
 six==1.12.0               # via faker, protobuf, pytest, python-dateutil
 text-unidecode==1.2       # via faker
+wcwidth==0.1.7            # via pytest