Support for erlang 26

[scohen]

I tried erlang 26.0.2, and lo and behold, it worked with lexical. There were a few unit test failures due to completion results being ordered differently, but otherwise, lexical works great under 26.

Fixes #244

[scottming]

Today, when I was trying version 26, I found that:

1. If Lexical is packaged with version 26 while the project is version 25, we won't be able to start Lexical.
2. There are no issues if Lexical is packaged with version 25 while the project is version 26.
3. There are no issues if Lexical is packaged with version 26 and the project is also version 26.

We may need to make a note of this in the documentation.

And this is the error:

~/Code/dummy master ?7 ❯ /Users/scottming/Code/lexical/_build/dev/package/lexical/bin/start_lexical.sh

11:08:40.826 [error] beam/beam_load.c(190): Error loading module 'Elixir.LoggerFileBackend':
  This BEAM file was compiled for a later version of the runtime system than the current (Erlang/OTP 25).
  To fix this, please re-compile this module with an Erlang/OTP 25 compiler.
  (Use of opcode 182; this emulator supports only up to 180.)



11:08:40.826 [error] Loading of /Users/scottming/Code/lexical/_build/dev/package/lexical/bin/../lib/logger_file_backend.ez/logger_file_backend/ebin/Elixir.LoggerFileBackend.beam failed: :badfile


11:08:40.842 [error] Loading of /Users/scottming/Code/lexical/_build/dev/package/lexical/bin/../lib/lx_sourceror.ez/lx_sourceror/ebin/Elixir.LXSourceror.beam failed: :badfile


11:08:40.842 [error] beam/beam_load.c(190): Error loading module 'Elixir.LXSourceror':
  This BEAM file was compiled for a later version of the runtime system than the current (Erlang/OTP 25).
  To fix this, please re-compile this module with an Erlang/OTP 25 compiler.
  (Use of opcode 182; this emulator supports only up to 180.)


** (ArgumentError) could not load module LXSourceror due to reason :badfile
    (elixir 1.15.4) lib/code.ex:1779: Code.ensure_loaded!/1
    (elixir 1.15.4) lib/enum.ex:984: Enum."-each/2-lists^foreach/1-0-"/2
    lib/lexical/server/boot.ex:17: LXical.Server.Boot.start/0
    nofile:1: (file)
    (stdlib 4.3.1.2) erl_eval.erl:748: :erl_eval.do_apply/7
    ```

[scohen]

I believe that the documentation makes this clear in the detailed installation instructions