Make lint target reliable

Previously only the files newer than the timestamp were passed to
the linter.

Changing the linter config or version did not trigger a lint of all
the files.

With this commit, all files are linted on changes.

Makefile

@@ -282,15 +282,15 @@ gh-pages:
 .build/ngeo-$(GITHUB_USERNAME)-gh-pages:
 	git clone --depth=1 --branch gh-pages $(GIT_REMOTE_URL) $@
 
-.build/eslint.timestamp: .build/node_modules.timestamp .eslintrc.yaml .eslintrc-es6.yaml \
+.build/eslint.timestamp: package.json .build/node_modules.timestamp .eslintrc.yaml .eslintrc-es6.yaml \
 		$(SRC_JS_FILES) \
 		$(TEST_JS_FILES) \
 		$(GMF_TEST_JS_FILES) \
 		$(EXAMPLES_JS_FILES) \
 		$(GMF_SRC_JS_FILES) \
 		$(GMF_EXAMPLES_JS_FILES) \
 		$(GMF_APPS_JS_FILES)
-	./node_modules/.bin/eslint $(filter-out .build/node_modules.timestamp .eslintrc.yaml .eslintrc-es6.yaml, $?)
+	./node_modules/.bin/eslint $(filter-out package.json .build/node_modules.timestamp .eslintrc.yaml .eslintrc-es6.yaml, $^)
 	touch $@
 
 dist/ngeo.js: .build/ngeo.json \