fixes bash parameter expansion (#1535)

Author: baldwicc

script-library/python-debian.sh

@@ -16,7 +16,7 @@ USERNAME=${4:-"automatic"}
 UPDATE_RC=${5:-"true"}
 INSTALL_PYTHON_TOOLS=${6:-"true"}
 USE_ORYX_IF_AVAILABLE=${7:-"true"}
-OPTIMIZE_BUILD_FROM_SOURCE=${8-"false"}
+OPTIMIZE_BUILD_FROM_SOURCE=${8:-"false"}
 
 DEFAULT_UTILS=("pylint" "flake8" "autopep8" "black" "yapf" "mypy" "pydocstyle" "pycodestyle" "bandit" "pipenv" "virtualenv")
 PYTHON_SOURCE_GPG_KEYS="64E628F8D684696D B26995E310250568 2D347EA6AA65421D FB9921286F5E1540 3A5CA953F73C700D 04C367C218ADD4FF 0EDDC5F26A45C816 6AF053F07D9DC8D2 C9BE28DEE6DF025C 126EB563A74B06BF D9866941EA5BBD71 ED9D77D5"