Detect attempts to install packages for an older version of elm

[opsb]

At the moment there's a kernel panick

$ elm --version
0.19.0

$ elm-json --version
elm-json 0.2.0

$ RUST_BACKTRACE=1 elm-json install krisajenkins/elm-dialog
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:345:21
stack backtrace:
   0: start
   1: start
   2: start
   3: start
   4: start
   5: start
   6: start
   7: start
   8: start
   9: start
  10: start
  11: start
  12: start
  13: start
  14: main
  15: start
  16: main

krisajenkins/elm-dialog has never been updated to work with 0.19