Fix ls-files matching regexp

As splitting by NUL means to allow the file names to contain
newlines, path names should match at beginning-of-string instead
of beginning-of-line.

Author: nobu

optparse.gemspec

@@ -21,9 +21,9 @@ Gem::Specification.new do |spec|
   spec.metadata["source_code_uri"] = spec.homepage
 
   spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
-    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{\A(?:test|spec|features)/}) }
   end
   spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.executables   = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 end