Fix problem with make coverage

Makefile

@@ -472,7 +472,7 @@ testdox: .check-foundation
 coverage: .check-foundation
 	@cd `$(CONFIG_TOOL) test-folder`;phpunit --testdox --coverage-html=reports/coverage --coverage-text .
 	@echo "Done. Reports also available on `$(CONFIG_TOOL) test-folder`/reports/coverage/index.html"
-	@make .open-document url=reports/coverage/index.html
+	@make -f ../Makefile .open-document url=reports/coverage/index.html
 
 cs-fixer: .check-foundation
 	@cd `$(CONFIG_TOOL) library-folder`;${FOUNDATION_HOME}/php-cs-fixer -v fix --level=all --fixers=indentation,linefeed,trailing_spaces,unused_use,return,php_closing_tag,short_tag,visibility,braces,extra_empty_lines,phpdoc_params,eof_ending,include,controls_spaces,elseif .