Relax gem version requirement for unicode-display_width

[mjankowski]

Resolves #138

I think this is harmless ... bundled with 2.x version, specs passed; relaxed gemspec, bumped bundle, ran specs again ... seems ok?

[pboling]

I need this change as well, because simplecov-console depends on this gem. Hopefully it can be released as a patch.
Worth noting that current release of rubocop has the following dependency on unicode-display_width

  s.add_dependency('unicode-display_width', '>= 2.4.0', '< 4.0')

Does it make sense to match that, since it is going to be present in a majority of Gemfiles? Excluding v1 might prevent a patch release with a strict interpretation of SemVer though.
ref: https://github.com/rubocop/rubocop/blob/master/rubocop.gemspec#L42C1-L43C1

CC @nateberkopec @tj

[tagliala]

Rubocop is now allowing unicode-display_width v3

This would fix an unexpected downgrade of terminal-table from 3.0.2 to 1.6.0 when using rubocop + i18n-tasks together

-    terminal-table (3.0.2)
-      unicode-display_width (>= 1.1.1, < 3)
+    terminal-table (1.6.0)
     thor (1.3.2)
     tilt (2.5.0)
     timeout (0.4.3)
@@ -721,7 +720,9 @@ GEM
       ethon (>= 0.9.0)
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
-    unicode-display_width (2.6.0)
+    unicode-display_width (3.1.3)
+      unicode-emoji (~> 4.0, >= 4.0.4)
+    unicode-emoji (4.0.4)
     uniform_notifier (1.16.0)