Fix issue 2450 ipv6 SC2102 warning

[gengwg]

This is attempt to fix issue 2450 here:

#2450

Test

Test script:

$ cat test.sh
#!/bin/bash
curl -k https://[2620:10d:c0a8:2b::127]/

Before:

$ which shellcheck
/Users/gengwg/.cabal/bin/shellcheck

$ shellcheck -V
ShellCheck - shell script analysis tool
version: 0.8.0
license: GNU General Public License, version 3
website: https://www.shellcheck.net

$ shellcheck test.sh

In test.sh line 2:
curl -k https://[2620:10d:c0a8:2b::127]/
                ^---------------------^ SC2102 (info): Ranges can only match single chars (mentioned due to duplicates).

For more information:
  https://www.shellcheck.net/wiki/SC2102 -- Ranges can only match single char...

After:

Test:

$ cabal test
Resolving dependencies...
Build profile: -w ghc-8.10.7 -O1
In order, the following will be built (use -v for more details):
 - ShellCheck-0.8.0 (lib) (first run)
 - ShellCheck-0.8.0 (test:test-shellcheck) (first run)
Configuring library for ShellCheck-0.8.0..
Preprocessing library for ShellCheck-0.8.0..
Building library for ShellCheck-0.8.0..
....
[1 of 1] Compiling Main             ( test/shellcheck.hs, /Users/gengwg/github/shellcheck/dist-newstyle/build/x86_64-osx/ghc-8.10.7/ShellCheck-0.8.0/t/test-shellcheck/build/test-shellcheck/test-shellcheck-tmp/Main.o )
Linking /Users/gengwg/github/shellcheck/dist-newstyle/build/x86_64-osx/ghc-8.10.7/ShellCheck-0.8.0/t/test-shellcheck/build/test-shellcheck/test-shellcheck ...
Running 1 test suites...
Test suite test-shellcheck: RUNNING...
Test suite test-shellcheck: PASS
Test suite logged to:
/Users/gengwg/github/shellcheck/dist-newstyle/build/x86_64-osx/ghc-8.10.7/ShellCheck-0.8.0/t/test-shellcheck/test/ShellCheck-0.8.0-test-shellcheck.log
1 of 1 test suites (1 of 1 test cases) passed.

$ cabal install --overwrite-policy=always
Wrote tarball sdist to
/Users/gengwg/shellcheck/dist-newstyle/sdist/ShellCheck-0.8.0.tar.gz
Resolving dependencies...
Up to date
Symlinking 'shellcheck' to '/Users/gengwg/.cabal/bin/shellcheck'

Check again:

$ shellcheck ~/test.sh
<no output now>

[koalaman]

Closing this as explained in #2450