test: disable nyc's translation cache

NYC caches the instrumented sources, but doesn't know that we patch NYC (at
`yarn install` time) to accept options that control the injected measurement
code. If you upgrade to this branch, then immediately run `yarn test-nyc`
without first doing a top-level `yarn` (install), you'll get incorrectly
instrumented code in the cache, and a subsequent `yarn` (install) won't clear
out the cache.

It seems like the cache doesn't speed up e.g. `zoe/test/unitTests` by more
than about 10%, so I'm disabling it to reduce some of the inevitable
confusion we'll get as we cut over. We might re-enable it later once
everybody's trees are updated.

Author: warner

.nycrc.yaml

@@ -3,6 +3,7 @@
 # file, while never touching a second, will look like it covers everything,
 # when really half the source code is ignored.
 all: true
+cache: false
 
 # only report on files in each package's "src/" directory, not things in
 # node_modules/ or helpers in test/