[README] Supported Node.js versions for SDK development (#1359)
[README] Supported Node.js versions for SDK development (#1359)

Several dependencies currently have a `<=9` requirement on the Node.js engine version. The way the README is written, it may give people the impression that any version above 8 is also supported, but that's not the case for Node.js 10 and 11.
jsayol/firebase-js-sdk,jsayol/firebase-js-sdk,jsayol/firebase-js-sdk,jsayol/firebase-js-sdk,jsayol/firebase-js-sdk