gu install -c org.graalvm.ruby is now gu install org.graalvm.ruby

(cherry picked from commit 5aaaa62)

Author: chrisseaton

doc/user/installing.md

@@ -54,7 +54,7 @@ This is done using the `gu` command. The Ruby package is the same for both
 editions of GraalVM and comes from GitHub.
 
 ```
-$ gu install -c org.graalvm.ruby
+$ gu install org.graalvm.ruby
 ```
 
 Or download manually from https://github.com/oracle/truffleruby/releases.

tool/jt.rb

@@ -1990,7 +1990,7 @@ def dockerfile(*args)
       lines.push "RUN curl -OL https://github.com/oracle/graal/releases/download/vm-#{public_version}/graalvm-ce-#{public_version}-linux-amd64.tar.gz"
       lines.push "RUN tar -zxf graalvm-ce-#{public_version}-linux-amd64.tar.gz"
       lines.push "ENV GRAALVM_BASE=/test/graalvm-#{public_version}"
-      lines.push "RUN $GRAALVM_BASE/bin/gu install -c org.graalvm.ruby"
+      lines.push "RUN $GRAALVM_BASE/bin/gu install org.graalvm.ruby"
       lines.push "ENV D_RUBY_BASE=$GRAALVM_BASE/jre/languages/ruby"
       lines.push "ENV D_RUBY_BIN=$GRAALVM_BASE/bin"
     when :graalvm