DOC: Updated Conan version.

doc/DEPENDENCIES.md

 # Dependencies #
 
+Exact versions of some packages here are listed in `requirements.txt`.
+
 ## General ##
 
 ```
->=conan-1.50.0 (e.g. with `pip install conan`)
+>=conan-1.54.0 (e.g. with `pip install conan`)
 >=cmake-3.13
 >=gcc-10.2.0 | >=clang-11
 ```