Installation error on macOS Mojave

[alexreg]

$ sudo gem install imsg
Fetching: rb-appscript-0.6.1.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing imsg:
	ERROR: Failed to build gem native extension.

    current directory: /Library/Ruby/Gems/2.3.0/gems/rb-appscript-0.6.1
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20190224-45868-sj77rw.rb extconf.rb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/$(RUBY_BASE_NAME)
extconf.rb:44:in `<main>': uninitialized constant Config (NameError)
Did you mean?  RbConfig
               CONFIG

extconf failed, exit code 1

Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/rb-appscript-0.6.1 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/rb-appscript-0.6.1/gem_make.out
!1
****

[CodingErik]

yea, had this same issue here