Bump Linux build dependencies

* Python 3.7.2 to 3.7.4
* Docker 18.09.5 to 18.09.7
* Alpine 3.9.3 to 3.10.0
* Debian stretch-20190326 to stretch-20190708

Signed-off-by: Christopher Crone <[email protected]>

Dockerfile

@@ -1,9 +1,9 @@
-ARG DOCKER_VERSION=18.09.5
-ARG PYTHON_VERSION=3.7.3
-ARG BUILD_ALPINE_VERSION=3.9
+ARG DOCKER_VERSION=18.09.7
+ARG PYTHON_VERSION=3.7.4
+ARG BUILD_ALPINE_VERSION=3.10
 ARG BUILD_DEBIAN_VERSION=slim-stretch
-ARG RUNTIME_ALPINE_VERSION=3.9.3
-ARG RUNTIME_DEBIAN_VERSION=stretch-20190326-slim
+ARG RUNTIME_ALPINE_VERSION=3.10.0
+ARG RUNTIME_DEBIAN_VERSION=stretch-20190708-slim
 
 ARG BUILD_PLATFORM=alpine