Update basically configuration for gemspec

Author: hsbt

cmath.gemspec

@@ -2,22 +2,22 @@
 Gem::Specification.new do |spec|
   spec.name          = "cmath"
   spec.version       = "0.0.1"
-  spec.authors       = ["SHIBATA Hiroshi"]
-  spec.email         = ["hsbt@ruby-lang.org"]
+  spec.date          = '2017-02-02'
+  spec.authors       = ["Tadayoshi Funaba"]
+  spec.email         = [nil]
 
-  spec.summary       = %q{TODO: Write a short summary, because Rubygems requires one.}
-  spec.description   = %q{TODO: Write a longer description or delete this line.}
-  spec.homepage      = "TODO: Put your gem's website or public repo URL here."
+  spec.summary       = "Provides Trigonometric and Transcendental functions for complex numbers"
+  spec.description   = "CMath is a library that provides trigonometric and transcendental functions for complex numbers. The functions in this module accept integers, floating-point numbers or complex numbers as arguments."
+  spec.homepage      = "https://github.com/ruby/cmath"
   spec.license       = "BSD-2-Clause"
 
-  spec.files         = `git ls-files -z`.split("\x0").reject do |f|
-    f.match(%r{^(test|spec|features)/})
-  end
+  spec.files         = "lib/cmath.rb"
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
+  spec.required_ruby_version = ">= 2.5.0dev"
 
-  spec.add_development_dependency "bundler", "~> 1.14"
-  spec.add_development_dependency "rake", "~> 10.0"
-  spec.add_development_dependency "minitest", "~> 5.0"
+  spec.add_development_dependency "bundler"
+  spec.add_development_dependency "rake"
+  spec.add_development_dependency "minitest"
 end