Remove references to node 9 errors in readme

Node 9.x seems no longer relevant since we are now directing devs to use
`nvm install --latest-npm` (currently v.12.6.0)

Author: mchowning

README.md

@@ -41,12 +41,6 @@ nvm install --latest-npm
 yarn install
 ```
 
-Note: using node v9.x currently produces the following error:
-```
-error sane@3.1.0: The engine "node" is incompatible with this module. Expected version "6.* || 8.* || >= 10.*".
-```
-To be revisited, as we don't need to impose a limit in version per se.
-
 ## Run
 
 ```