Update prebuildify and node-gyp-build

[vweevers]

Tackles the final items of #575. Alpine and iOS are yet to do but we have a separate issues for those (#388 and #626). Supersedes #622.

Semver-minor because of the added armv tag.

Once prebuild/docker-images#5 lands and is built+pushed, I'll temporarily modify our .travis.yml here to enable the arm job without uploading prebuilds. IMO we don't have to smoke-test a release again.

[vweevers]

Also closes #388.

[vweevers]

ARM ✔️ (took 5 min 58 sec)

$ file prebuilds/*/*
prebuilds/android-arm64/node.napi.armv8.node: ELF 64-bit LSB  shared object, ARM aarch64, version 1 (SYSV), dynamically linked, stripped
prebuilds/android-arm/node.napi.armv7.node:   ELF 32-bit LSB  shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, stripped
prebuilds/linux-arm64/node.napi.armv8.node:   ELF 64-bit LSB  shared object, ARM aarch64, version 1 (SYSV), dynamically linked, stripped
prebuilds/linux-arm/node.napi.armv7.node:     ELF 32-bit LSB  shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, stripped

Alpine ✔️ (took 1 min 35 sec)

$ file prebuilds/*/*
prebuilds/linux-x64/node.napi.musl.node: ELF 64-bit LSB  shared object, x86-64, version 1 (SYSV), dynamically linked, stripped