Issue #144 - Update Pabot to version 0.53

* Updated the Dockerfile

Author: ppodgorsek

Dockerfile

@@ -21,7 +21,7 @@ ENV CHROMIUM_VERSION 73.0.*
 ENV FAKER_VERSION 4.2.0
 ENV FIREFOX_VERSION 66.0*
 ENV GECKO_DRIVER_VERSION v0.22.0
-ENV PABOT_VERSION 0.46
+ENV PABOT_VERSION 0.53
 ENV PYTHON_PIP_VERSION 18.0*
 ENV REQUESTS_VERSION 0.5.0
 ENV ROBOT_FRAMEWORK_VERSION 3.1.1