Fix a few typos (#2697)

doc/TUTORIAL.md

doc/service-tests.md

lib/sys/prometheus-metrics.js

services/base-non-memory-caching.js

services/bower/bower.tester.js

services/dynamic/dynamic-json.tester.js

services/dynamic/dynamic-xml.tester.js

services/dynamic/dynamic-yaml.tester.js

services/github/github-pull-request-check-state.tester.js

services/jenkins/jenkins-plugin-installs.tester.js

services/luarocks/luarocks-version.js

services/pypi/pypi.tester.js

services/vaadin-directory/vaadin-directory.tester.js

services/vscode-marketplace/vscode-marketplace.service.js

services/waffle/waffle.tester.js