Update to latest paradox (#159)

For some reason I can't resolve 0.2.13.

Author: dwijnand

documentation/documentation.sbt

@@ -1,3 +1,4 @@
+enablePlugins(ParadoxPlugin)
 enablePlugins(ParadoxSitePlugin)
 siteSubdirName in Paradox := ""
 paradoxTheme := Some(builtinParadoxTheme("generic"))

project/plugins.sbt

@@ -6,4 +6,4 @@ addSbtPlugin("de.heikoseeberger"     % "sbt-header"          % "5.2.0")
 addSbtPlugin("org.xerial.sbt"        % "sbt-sonatype"        % "2.3")
 addSbtPlugin("com.jsuereth"          % "sbt-pgp"             % "1.1.2")
 addSbtPlugin("com.typesafe"          % "sbt-mima-plugin"     % "0.3.0")
-addSbtPlugin("com.lightbend.paradox" % "sbt-paradox"         % "0.2.13")
+addSbtPlugin("com.lightbend.paradox" % "sbt-paradox"         % "0.5.3")