Fixup TypeScript build, and sourcemap filename bug

[guybedford]

This fixes #237, adding a console log of the TypeScript version being used in the build:

ncc: Using typescript@3.2.2 (ncc built-in)
# or
ncc: Using typescript@3.2.2 (local user-provided)

It also resolves the bug in master with the error Error: ENOENT: no such file or directory, open '/usr/local/lib/node_modules/@zeit/ncc/dist/ncc/source-register.js.cache.js' due to a file name typo.

[codecov-io]

Codecov Report

Merging #244 into master will not change coverage.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master     #244   +/-   ##
=======================================
  Coverage   69.25%   69.25%           
=======================================
  Files          16       16           
  Lines         670      670           
=======================================
  Hits          464      464           
  Misses        206      206

Impacted Files	Coverage Δ
src/loaders/ts-loader.js	88.88% <50%> (ø)	⬆️

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