build: use clang-format from npm

PR-URL: #276
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

package.json

@@ -26,7 +26,7 @@
     "codecov-upload-js": "codecov --disable=gcov --file=coverage-js.lcov",
     "codecov-upload": "npm run codecov-upload-cc && npm run codecov-upload-js",
     "linter": "node scripts/linter.js",
-    "format": "clang-format -i src/*"
+    "format": "npx clang-format -i src/*"
   },
   "repository": {
     "type": "git",