Fix npm install so that it's not necessary to use deprecated dependency resolution

[SamClayton]

--legacy-peer-deps

[SamClayton]

Current situation on react-16.0.0-migration branch:

npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! Found: react@16.14.0
npm ERR! node_modules/react
npm ERR! react@"^16.14.0" from the root project
npm ERR! peer react@"^0.14.0 || ^15.0.0 || 16.x" from react-container-dimensions@1.4.1
npm ERR! node_modules/react-container-dimensions
npm ERR! dev react-container-dimensions@"^1.4.1" from the root project
npm ERR! 8 more (react-dom, react-extras, react-fuzzy, react-ga, ...)
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer react@"0.14.x || ^15.0.0-rc" from react-clickdrag@3.0.2
npm ERR! node_modules/react-number-editor/node_modules/react-clickdrag
npm ERR! react-clickdrag@"^3.0.2" from react-number-editor@4.0.3
npm ERR! node_modules/react-number-editor
npm ERR! react-number-editor@"^4.0.3" from the root project

[SamClayton]

Currently don't need to use this switch on develop branch, but not sure if that applies to others.