Add libgmp as a dependency for rubyinstaller

appveyor.yml

@@ -9,7 +9,7 @@ install:
   - c:/msys64/usr/bin/bash -lc "pacman -Sy --noconfirm"
   # Update ruby dependencies, because the pre-installed are outdated.
   # Keep this in sync with the "depends" list in PKGBUILD files.
-  - c:/msys64/usr/bin/bash -lc "pacman -S --noconfirm --needed ${MINGW_PACKAGE_PREFIX}-toolchain ${MINGW_PACKAGE_PREFIX}-gcc-libs ${MINGW_PACKAGE_PREFIX}-gdbm ${MINGW_PACKAGE_PREFIX}-libffi ${MINGW_PACKAGE_PREFIX}-libyaml ${MINGW_PACKAGE_PREFIX}-openssl ${MINGW_PACKAGE_PREFIX}-zlib"
+  - c:/msys64/usr/bin/bash -lc "pacman -S --noconfirm --needed ${MINGW_PACKAGE_PREFIX}-toolchain ${MINGW_PACKAGE_PREFIX}-gcc-libs ${MINGW_PACKAGE_PREFIX}-gdbm {MINGW_PACKAGE_PREFIX}-gmp ${MINGW_PACKAGE_PREFIX}-libffi ${MINGW_PACKAGE_PREFIX}-libyaml ${MINGW_PACKAGE_PREFIX}-openssl ${MINGW_PACKAGE_PREFIX}-zlib"
 
 build_script:
   - set PATH=C:/ruby%build_ruby%/bin;%PATH%