Revert "Preserve the npm cache on Travis"
Revert "Preserve the npm cache on Travis"

This reverts commit 22b874b10051c20b3c8271227d275b9098ba5145.

Was curious to try this, but it turns out to take longer to
download + persist the cache than it does to just download
the packages every time.

kensho/babel-preset-kensho,kensho/babel-preset-kensho