infra: fix typo in release buildspec. (#363)

Author: nadiaya

buildspec-release.yml

@@ -12,7 +12,7 @@ phases:
       # run unit tests
       - AWS_ACCESS_KEY_ID= AWS_SECRET_ACCESS_KEY= AWS_SESSION_TOKEN=
         AWS_CONTAINER_CREDENTIALS_RELATIVE_URI= AWS_DEFAULT_REGION=
-        tox -e py27,py36,p37 --parallel all -- test/unit
+        tox -e py27,py36,py37 --parallel all -- test/unit
 
       # run local integ tests
       #- $(aws ecr get-login --no-include-email --region us-west-2)