minor perf improvements

Closes Homebrew/homebrew#47224.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

Library/Homebrew/cmd/bottle.rb

@@ -36,7 +36,8 @@ MAXIMUM_STRING_MATCHES = 100
 
 module Homebrew
   def keg_contains(string, keg, ignores)
-    @put_string_exists_header, @put_filenames = nil
+    @put_string_exists_header = nil
+    @put_filenames = nil
 
     def print_filename(string, filename)
       unless @put_string_exists_header

Library/Homebrew/cmd/doctor.rb

@@ -1298,13 +1298,14 @@ module Homebrew
 
     first_warning = true
     methods.each do |method|
-      begin
-        out = checks.send(method)
-      rescue NoMethodError
+      unless checks.respond_to?(method)
         Homebrew.failed = true
         puts "No check available by the name: #{method}"
         next
       end
+
+      out = checks.send(method)
+
       unless out.nil? || out.empty?
         if first_warning
           $stderr.puts <<-EOS.undent

Library/Homebrew/cmd/pull.rb

@@ -59,7 +59,7 @@ module Homebrew
         url = "https://github.com/Homebrew/homebrew/pull/#{arg}"
         tap = CoreFormulaRepository.instance
       elsif (testing_match = arg.match %r{brew.sh/job/Homebrew.*Testing/(\d+)/})
-        _, testing_job = *testing_match
+        testing_job = testing_match[1]
         url = "https://github.com/Homebrew/homebrew/compare/master...BrewTestBot:testing-#{testing_job}"
         tap = CoreFormulaRepository.instance
         odie "Testing URLs require `--bottle`!" unless ARGV.include?("--bottle")

Library/Homebrew/compilers.rb

@@ -33,7 +33,7 @@ class CompilerFailure
   def self.create(spec, &block)
     # Non-Apple compilers are in the format fails_with compiler => version
     if spec.is_a?(Hash)
-      _, major_version = spec.first
+      major_version = spec.first[1]
       name = "gcc-#{major_version}"
       # so fails_with :gcc => '4.8' simply marks all 4.8 releases incompatible
       version = "#{major_version}.999"

Library/Homebrew/formula.rb

@@ -1271,7 +1271,7 @@ class Formula
         "root_url" => bottle_spec.root_url,
       }
       bottle_info["files"] = {}
-      bottle_spec.collector.keys.each do |os|
+      bottle_spec.collector.each_key do |os|
         checksum = bottle_spec.collector[os]
         bottle_info["files"][os] = {
           "url" => "#{bottle_spec.root_url}/#{Bottle::Filename.create(self, os, bottle_spec.revision)}",

Library/Homebrew/utils/json.rb

@@ -24,7 +24,8 @@ module Utils
         obj.inject({}) do |result, (key, val)|
           key = key.respond_to?(:to_s) ? key.to_s : key
           val = stringify_keys(val)
-          result.merge!(key => val)
+          result[key] = val
+          result
         end
       else
         obj