gem install curb　ができない。エラー

curbを使いたいのですが、gem install curbをやっても上手くインストールすることができません。

下のサイトを参考に次のコードを試してみましたがエラーがでてしまいました。

Ruby
1gem install curb --version 0.7.18 --platform=ruby -- -- --with-curl-lib="C:/Ruby25-x64/bin" -
2-with-curl-include="C:/Ruby25-x64/includes"

参考サイト
http://wordpress.honobono-life.info/code/windows7%E3%81%ABcurb%EF%BC%88ruby%EF%BC%89%E3%82%92%E3%82%A4%E3%83%B3%E3%82%B9%E3%83%88%E3%83%BC%E3%83%AB%E3%81%99%E3%82%8B%E6%89%8B%E9%A0%86/

libcurl.dllとcurl.exeは/Ruby25-x64/binの直下に置いてあります。
どうしたら上手くインストールできるでしょうか？

ruby
1▼▼▼エラーメッセージ▼▼▼
2Temporarily enhancing PATH for MSYS/MINGW...
3Building native extensions with: '-- --with-curl-lib=C:/Ruby25-x64/bin --with-curl-include=C:/Ruby25-x64/includes'
4This could take a while...
5ERROR:  Error installing curb:
6        ERROR: Failed to build gem native extension.
7
8    current directory: C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/curb-0.7.18/ext
9C:/Ruby25-x64/bin/ruby.exe -r ./siteconf20190416-3216-1oii1yc.rb extconf.rb -- --with-curl-lib=C:/Ruby25-x64/bin --with-c
10url-include=C:/Ruby25-x64/includes
11checking for curl-config... no
12checking for -lcurl... yes
13checking for curl/curl.h... no
14*** extconf.rb failed ***
15Could not create Makefile due to some reason, probably lack of necessary
16libraries and/or headers.  Check the mkmf.log file for more details.  You may
17need configuration options.
18
19Provided configuration options:
20        --with-opt-dir
21        --without-opt-dir
22        --with-opt-include
23        --without-opt-include=${opt-dir}/include
24        --with-opt-lib
25        --without-opt-lib=${opt-dir}/lib
26        --with-make-prog
27        --without-make-prog
28        --srcdir=.
29        --curdir
30        --ruby=C:/Ruby25-x64/bin/$(RUBY_BASE_NAME)
31        --with-curl-dir
32        --without-curl-dir
33        --with-curl-include=${curl-dir}/include
34        --with-curl-lib=${curl-dir}/lib
35        --with-curllib
36        --without-curllib
37extconf.rb:18:in `<main>':   Can't find libcurl or curl/curl.h (RuntimeError)
38
39  Try passing --with-curl-dir or --with-curl-lib and --with-curl-include
40  options to extconf.
41
42To see why this extension failed to compile, please check the mkmf.log which can be found here:
43To see why this extension failed to compile, please check the mkmf.log which 
44extconf.rb:18:in `<main>':   Can't find libcurl or curl/curl.h (Runtim
45eEr
46ror)
47
48  Try passing --with-curl-dir or --with-curl-lib and --with-curl-inclu
49de
50extconf.rb:18:in `<main>':   Can't find libcurl or curl/curl.h (Runt
51im
52eError)
53
54  Try passing --with-curl-dir or --with-curl-lib and --with-curl-inc
55lu
56extconf.rb:18:in `<main>':   Can't find libcurl or curl/curl.h (RuntimeError)
57
58  Try passing --with-curl-dir or --with-curl-lib and --with-curl-include
59  options to extconf.
60
61To see why this extension failed to compile, please check the mkmf.log which can be found here:
62
63  C:/Ruby25-x64/lib/ruby/gems/2.5.0/extensions/x64-mingw32/2.5.0/curb-0.7.18/mkmf.log
64
65extconf failed, exit code 1
66
67Gem files will remain installed in C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/curb-0.7.18 for inspection.
68Results logged to C:/Ruby25-x64/lib/ruby/gems/2.5.0/extensions/x64-mingw32/2.5.0/curb-0.7.18/gem_make.out
69