Move the Gemfile dependencies to the gemspec

.gitignore

@@ -9,3 +9,4 @@
 
 # rspec failure tracking
 .rspec_status
+/Gemfile.lock

Gemfile

@@ -4,9 +4,3 @@ source "https://rubygems.org"
 
 # Specify your gem's dependencies in nostr.gemspec
 gemspec
-
-gem "rake", "~> 13.0"
-
-gem "rspec", "~> 3.0"
-
-gem "rubocop", "~> 1.21"

nostr.gemspec

@@ -29,4 +29,8 @@ Gem::Specification.new do |spec|
   spec.bindir = "exe"
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
+
+  spec.add_development_dependency "rake", "~> 13.0"
+  spec.add_development_dependency "rspec", "~> 3.12"
+  spec.add_development_dependency "rubocop", "~> 1.42"
 end