Update README.md

README.md

@@ -10,7 +10,7 @@ How to build and debug the library during development.
 The following packages are required in order to build the library:
 * cmake 3.8+
   * gcc 7+/clang 7+/msvc 16+
-  * fmtlib 6.1.2+
+  * fmtlib 5.2.1+
   * pybind11 2.3.0+
 * python 3.6+
   * setuptools