Linter: Fix SC2223

This default assignment may cause DoS due to globbing. Quote it.

- https://github.com/koalaman/shellcheck/wiki/SC2223

Author: glensc

install-extensions.sh

@@ -2,10 +2,10 @@
 
 set -xeu
 
-: ${TRAVIS_PHP_VERSION=7.4}
-: ${TIDEWAYS_VERSION=4.1.4}
-: ${TIDEWAYS_XHPROF_VERSION=5.0.2}
-: ${PHP_VERSION=${TRAVIS_PHP_VERSION}}
+: "${TRAVIS_PHP_VERSION=7.4}"
+: "${TIDEWAYS_VERSION=4.1.4}"
+: "${TIDEWAYS_XHPROF_VERSION=5.0.2}"
+: "${PHP_VERSION=${TRAVIS_PHP_VERSION}}"
 
 die() {
 	echo >&2 "ERROR: $*"