Update jordan/icinga2 Docker tag to v2.13.7

This MR contains the following updates:

Package	Type	Update	Change
jordan/icinga2	final	patch	2.13.6 -> 2.13.7

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webserver/docker_icinga/templates/Dockerfile

@@ -13,7 +13,7 @@ RUN apt-get update \
     libnet-dns-perl \
     libnet-ip-perl \
     perl \
-    python-requests \
+    python3-requests \
     python3 \
     python3-paho-mqtt \
  && apt-get autoremove -y \