build: Switch conan packages from bincrafters to conan.io (boostorg#537)

Discussion at conan-io/conan-center-index#4151 (comment)

Fixes Azure Pipelines builds for boostorg#535

conanfile.txt

@@ -1,14 +1,14 @@
 #
-# Copyright (c) 2018-2019 Mateusz Loskot <mateusz at loskot dot net>
+# Copyright (c) 2018-2021 Mateusz Loskot <mateusz at loskot dot net>
 #
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at
 # http://www.boost.org/LICENSE_1_0.txt)
 #
 [requires]
-libpng/1.6.37@bincrafters/stable
-libjpeg/9c@bincrafters/stable
-libtiff/4.0.9@bincrafters/stable
+libjpeg/9d
+libpng/1.6.37
+libtiff/4.1.0
 
 [generators]
 cmake