В чём ошибка при установке Rails?

$ gem i rails
Temporarily enhancing PATH for MSYS/MINGW...
Building native extensions. This could take a while...
ERROR:  Error installing rails:
        ERROR: Failed to build gem native extension.

    current directory: D:/Ruby26-x64/lib/ruby/gems/2.6.0/gems/websocket-driver-0.7.1/ext/websocket-driver
D:/Ruby26-x64/bin/ruby.exe -I D:/Ruby26-x64/lib/ruby/2.6.0 -r ./siteconf20190912-8476-1pme8ot.rb extconf.rb
creating Makefile

current directory: D:/Ruby26-x64/lib/ruby/gems/2.6.0/gems/websocket-driver-0.7.1/ext/websocket-driver
make "DESTDIR=" clean

current directory: D:/Ruby26-x64/lib/ruby/gems/2.6.0/gems/websocket-driver-0.7.1/ext/websocket-driver
make "DESTDIR="
generating websocket_mask-x64-mingw32.def
make: *** No rule to make target '/D/Ruby26-x64/include/ruby-2.6.0/ruby.h', needed by 'websocket_mask.o'.  Stop.

make failed, exit code 2

Gem files will remain installed in D:/Ruby26-x64/lib/ruby/gems/2.6.0/gems/websocket-driver-0.7.1 for inspection.
Results logged to D:/Ruby26-x64/lib/ruby/gems/2.6.0/extensions/x64-mingw32/2.6.0/websocket-driver-0.7.1/gem_make.out