shinylive 0.5.0

Bug fixes and minor improvements

• Updated the default shinylive assets to
  v0.10.12,
  which upgrades the bundled webR to
  v0.6.0 (#193, #195).

• WebAssembly package binaries cached during export() are now replaced once
  the WebAssembly repository catches up to the locally installed version.
  Previously, a binary downloaded while the repository lagged behind was never
  refreshed (#194).