如何修复此错误？
osx:~ osx$ brew install imagemagick@6
==> Downloading https://homebrew.bintray.com/bottles/imagemagick@6-6.9.9-38.high_sierra.bottle.tar.gz
Already downloaded: /Users/osx/Library/Caches/Homebrew/imagemagick@6-6.9.9-38.high_sierra.bottle.tar.gz
==> Pouring imagemagick@6-6.9.9-38.high_sierra.bottle.tar.gz
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.
If you need to have this software first in your PATH run:
echo 'export PATH="/usr/local/opt/imagemagick@6/bin:$PATH"' >> ~/.bash_profile
For compilers to find this software you may need to set:
LDFLAGS: -L/usr/local/opt/imagemagick@6/lib
CPPFLAGS: -I/usr/local/opt/imagemagick@6/include
For pkg-config to find this software you may need to set:
PKG_CONFIG_PATH: /usr/local/opt/imagemagick@6/lib/pkgconfig
==> Summary
/usr/local/Cellar/imagemagick@6/6.9.9-38: 1,471 files, 23.0MB
osx:~ osx$ brew link imagemagick
Error: No such keg: /usr/local/Cellar/imagemagick
osx:~ osx$