Fix variable reference in deploy hook condition

[alexislefebvre]

Why

The dollar sign was missing.

This looked like it would not expand the variable.

See other examples that use a $:

platformsh-docs/sites/upsun/src/get-started/stacks/flask.md

Line 67 in cdddbda

if [ "$PLATFORM_ENVIRONMENT_TYPE" = "production" ]; then

platformsh-docs/sites/platform/src/development/variables/use-variables.md

Lines 376 to 378 in cdddbda

	if [ "$PLATFORM_ENVIRONMENT_TYPE" = production ] ; then
	echo "This is live on production"
	else if [ "$PLATFORM_ENVIRONMENT_TYPE" = staging ] ; then

What's changed

Where are changes

Updates are for:

• platform (sites/platform templates)
• upsun (sites/upsun templates)