Installation on Windows does not move DLLs to output folder

**Describe the bug**
I use `vcpkg` to install Drogon's prerequisites. Building Drogon with `cmake` works just fine, but installing with `cmake` does not copy the required DLLs to the output `bin/` directory.

**To Reproduce**
Steps to reproduce the behavior:
1. `cd build`
2. `cmake -DCMAKE_TOOLCHAIN_FILE=[path to]/vcpkg/scripts/buildsystems/vcpkg.cmake -DCMAKE_INSTALL_PREFIX=[path to]/install ..`
3. `cmake --build .`
4. `cmake --install . --config Debug`
5. Runing `install/bin/drogon_ctl.exe` will fail since the required DLLs were not moved to `install/bin`

**Expected behavior**
`drogon_ctl.exe` should display its help page. DLLs listed by `dumpbin /dependents install/bin/drogon_ctl.exe` should be found.

**Desktop (please complete the following information):**
- OS: Windows 10