Bump minimum version of TS (i.e. deprecate old versions of TS) #1774
Description
Our current "supported" version range for typescript is
typescript-eslint/package.json
Line 77 in c82d121
Supporting as old as 3.2.1 puts a burden on us in regards to the typescript APIs that we're able to use.
3.2.1 was published November 29, 2018, and it doesn't support some the APIs we want to use for performance improvements (eg #1759).
We should review with the help of the TS folks to determine a "good enough" minimum version to set for our (eventual) 3.0.0 release.