dep: update to rake-compiler-dock 1.4.0 final

Author: flavorjones

Gemfile

@@ -4,7 +4,7 @@ gemspec
 
 gem("minitest", "5.20.0")
 gem("rake-compiler", "1.2.5")
-gem("rake-compiler-dock", "1.4.0.rc2")
+gem("rake-compiler-dock", "1.4.0")
 gem("rdoc", "6.6.2")
 
 gem("ruby_memcheck", "2.3.0") if Gem::Platform.local.os == "linux"