not use proxy for yarn command while build

[phuongnq]

Ticket reference or full description of what's in the PR

Issue while building under proxy

[INFO] --- frontend-maven-plugin:1.7.6:yarn (install legacy hybrid deps) @ crafter-studio ---
[INFO] Found proxies: [httpproxy{protocol='http', host='proxy-host', port=proxy-port}, httpsproxy{protocol='https', host='proxy-host', port=proxy-port}]
[INFO] Running 'yarn ' in /Users/phuong.nguyen/craftercms-dev/craftercms/src/studio-ui/ui/legacy
[INFO] yarn install v1.21.1
[INFO] [1/4] Resolving packages...
[INFO] success Already up-to-date.
[INFO] Done in 0.26s.
[INFO]
[INFO] --- frontend-maven-plugin:1.7.6:yarn (build legacy hybrid files) @ crafter-studio ---
[INFO] Found proxies: [httpproxy{protocol='http', host='prox-host', port=proxy-port}, httpsproxy{protocol='https', host='proxy-host', port=proxy-port}]
[INFO] Running 'yarn build --https-proxy=http://prox-host:proxy-port --proxy=http://prox-host:proxy-port' in /Users/phuong.nguyen/craftercms-dev/craftercms/src/studio-ui/ui/legacy
[INFO] yarn run v1.21.1
[INFO] $ babel ./src -d ../../static-assets --https-proxy=http://prox-host:proxy-port --proxy=http://prox-host:proxy-port
[ERROR] error: unknown option '--https-proxy'
[ERROR] error Command failed with exit code 1.
[INFO] info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  02:12 min
[INFO] Finished at: 2020-01-23T11:57:39+09:00

Related issue:
eirslett/frontend-maven-plugin#796

Work around:
Not use proxy for yarn command:
https://github.com/eirslett/frontend-maven-plugin#proxy-settings