tests: Make sure PATH is set for 'env -i'

/bin/ and /usr/bin/ are not searched by default on all platforms,
e.g. on cygwin:

  $ env -i zsh
  env: ‘zsh’: No such file or directory

Author: m0vie

Makefile

@@ -41,7 +41,7 @@ test:
 	for test in highlighters/*; do \
 		if [ -d $$test/test-data ]; then \
 			echo "Running test $${test##*/}"; \
-			env -i QUIET=$$QUIET $${TERM:+"TERM=$$TERM"} $(ZSH) -f tests/test-highlighting.zsh "$${test##*/}"; \
+			env -i QUIET=$$QUIET $${TERM:+"TERM=$$TERM"} PATH="$$PATH" $(ZSH) -f tests/test-highlighting.zsh "$${test##*/}"; \
 			: $$(( result |= $$? )); \
 		fi \
 	done; \