Update Docker image location.

Author: MattBlissett

600.en.adoc

@@ -249,7 +249,7 @@ If you are familiar with software development tools you can build a document on
 
 [source,shell]
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-docker run --rm -it --user $(id -u):$(id -g) -v $PWD:/documents/ gbif/asciidoctor-toolkit
+docker run --rm -it --user $(id -u):$(id -g) -v $PWD:/documents/ docker.gbif.org/asciidoctor-toolkit
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 Assuming all is well, the resulting documents are in subdirectories coded by language (such as `en`), including both HTML and PDF files.  The output from the command should provide clues if there are problems.