Update rector and the used class namespace

Seems like the class alias for Rector\Core is removed in 19.2 This
should fix the rector runs on github.

Rector to rename print to echo calls

deprecate ptln()

This method was used to ensure some basic readability in the created
HTML sources long before Firebug and later the builtin inspector tools
in browsers pretty printed the HTML for y

deprecate ptln()

This method was used to ensure some basic readability in the created
HTML sources long before Firebug and later the builtin inspector tools
in browsers pretty printed the HTML for you. Today, this is no longer
needed.

This adds a custom rector rule to automatically change all occurances to
echo statements.

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