Bump shellcheck to version 0.8.0 in docker image

And fix the new SC2295 warning.

test/Dockerfile

@@ -2,7 +2,7 @@ FROM ubuntu:18.04
 MAINTAINER Tim Byrne <sultan@locehilios.com>
 
 # Shellcheck and esh versions
-ARG SC_VER=0.7.1
+ARG SC_VER=0.8.0
 ARG ESH_VER=0.3.0
 
 # Install prerequisites and configure UTF-8 locale

test/conftest.py

@@ -25,7 +25,7 @@ def pytest_addoption(parser):
 @pytest.fixture(scope='session')
 def shellcheck_version():
     """Version of shellcheck supported"""
-    return '0.7.1'
+    return '0.8.0'
 
 
 @pytest.fixture(scope='session')