.travis.yml: fix typo in configure arguments

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65143 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

.travis.yml

@@ -64,7 +64,7 @@ matrix:
       compiler: clang
       # We are not going to make rdoc here; that is to be done above.
       env:
-        - "CONFIG_FLAG='--disable-install-docs --with-opt-dir=/usr/local/opt/openssl@1.1:/usr/local/opt/zlib'"
+        - "CONFIG_FLAG='--disable-install-doc --with-opt-dir=/usr/local/opt/openssl@1.1:/usr/local/opt/zlib'"
       before_install:
         - "JOBS=-j`sysctl -n hw.activecpu`"
         # Bare "brew update" nukes everything.