:lipstick: catch Travis CI checks

Run against markdownfmt.sh and remove an extra line.

perl/content.md

@@ -50,4 +50,3 @@ ONBUILD COPY . /usr/src/app
 ```
 
 Building this as a `perl:onbuild` image can let you reduce your project's `Dockerfile` into a single line of `FROM perl:onbuild`, which may be enough to build a stand-alone image for your project.
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