Fix npm commands in DockerTests.md (#21758)
Fix npm commands in DockerTests.md (#21758)

Summary:
[DOCS] [BUGFIX] [DockerTests.md] - Fix npm commands after https://github.com/facebook/react-native/pull/18597
Pull Request resolved: https://github.com/facebook/react-native/pull/21758

Differential Revision: D10366764

Pulled By: RSNara

fbshipit-source-id: 3b6050105df9eb99e7a591c7cc4fdec2ae25be9d

arthuralee/react-native,pandiaraj44/react-native,facebook/react-native,myntra/react-native,javache/react-native,exponentjs/react-native,javache/react-native,pandiaraj44/react-native,exponent/react-native,hammerandchisel/react-native,javache/react-native,hoangpham95/react-native,exponentjs/react-native,exponent/react-native,facebook/react-native,facebook/react-native,hammerandchisel/react-native,javache/react-native,myntra/react-native,janicduplessis/react-native,hammerandchisel/react-native,arthuralee/react-native,hammerandchisel/react-native,janicduplessis/react-native,hoangpham95/react-native,exponentjs/react-native,javache/react-native,hoangpham95/react-native,hoangpham95/react-native,facebook/react-native,arthuralee/react-native,exponent/react-native,exponent/react-native,myntra/react-native,exponentjs/react-native,exponent/react-native,hoangpham95/react-native,hammerandchisel/react-native,pandiaraj44/react-native,myntra/react-native,myntra/react-native,janicduplessis/react-native,exponentjs/react-native,exponent/react-native,janicduplessis/react-native,exponent/react-native,facebook/react-native,exponent/react-native,arthuralee/react-native,arthuralee/react-native,hammerandchisel/react-native,exponentjs/react-native,exponentjs/react-native,hoangpham95/react-native,janicduplessis/react-native,pandiaraj44/react-native,janicduplessis/react-native,myntra/react-native,pandiaraj44/react-native,myntra/react-native,janicduplessis/react-native,facebook/react-native,facebook/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,facebook/react-native,exponentjs/react-native,hoangpham95/react-native,pandiaraj44/react-native,hoangpham95/react-native,myntra/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,hammerandchisel/react-native,facebook/react-native,hammerandchisel/react-native,pandiaraj44/react-native,javache/react-native