Update mysql-connector-java to 8.0.15 (#271)

Author: scala-steward

build.sbt

@@ -8,7 +8,7 @@ scalacOptions ++= List("-encoding", "utf8", "-deprecation", "-feature", "-unchec
 libraryDependencies ++= Seq(
   "com.typesafe.play"       %% "play-doc"            % "2.0.0",
   "org.eclipse.jgit"        % "org.eclipse.jgit"     % "3.0.0.201306101825-r",
-  "mysql"                   % "mysql-connector-java" % "5.1.47",
+  "mysql"                   % "mysql-connector-java" % "8.0.15",
   "com.damnhandy"           % "handy-uri-templates"  % "2.1.7",
   "org.webjars"             % "jquery"               % "1.8.3",
   "org.webjars"             % "html5shiv"            % "3.7.3",