build: add quotes to run-npm-ci’s value

The Makefile contains two variable: NODE and run-npm-ci. Here’s the line
that sets the NODE variable:

  NODE ?= "$(PWD)/$(NODE_EXE)"

The value of the NODE variable contains quotation marks just in case
$(PWD) contains spaces. Before this change, here’s how the run-npm-ci
variable was set:

  run-npm-ci = $(PWD)/$(NPM) ci

The value of the run-npm-ci variable does not contain quotation marks.
$(run-npm-ci) is supposed expand into two words when interpreted by a
shell, but if $(PWD) contained spaces, then it would expand into more
than 2 words.

This change adds quotation marks to the value of run-npm-ci. This change
makes the Makefile more consistent and helps make sure that
$(run-npm-ci) does the right thing, even if $(PWD) contains spaces.

Author: Jayman2000

Makefile

@@ -788,7 +788,7 @@ out/doc/api/assets/%: doc/api_assets/% | out/doc/api/assets
 	@cp $< $@ ; $(RM) out/doc/api/assets/README.md
 
 
-run-npm-ci = $(PWD)/$(NPM) ci
+run-npm-ci = "$(PWD)/$(NPM)" ci
 
 LINK_DATA = out/doc/apilinks.json
 VERSIONS_DATA = out/previous-doc-versions.json