dockerfiles: upgrade to ubuntu:20.04

.maintain/docker/subkey.Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:stretch-slim
+FROM docker.io/library/ubuntu:20.04
 
 # metadata
 ARG VCS_REF
@@ -28,4 +28,3 @@ USER subkey
 RUN /usr/local/bin/subkey --version
 
 ENTRYPOINT ["/usr/local/bin/subkey"]
-

.maintain/docker/substrate.Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:stretch-slim
+FROM docker.io/library/ubuntu:20.04
 
 # metadata
 ARG VCS_REF
@@ -42,4 +42,3 @@ EXPOSE 30333 9933 9944
 VOLUME ["/substrate"]
 
 ENTRYPOINT ["/usr/local/bin/substrate"]
-

README.md

@@ -4,13 +4,12 @@
   <img src="/docs/media/sub.gif">
 </p>
 
-
 Substrate is a next-generation framework for blockchain innovation 🚀.
 
 ## Trying it out
 
-Simply go to [substrate.dev](https://substrate.dev) and follow the 
-[installation](https://substrate.dev/docs/en/knowledgebase/getting-started/) instructions. You can 
+Simply go to [substrate.dev](https://substrate.dev) and follow the
+[installation](https://substrate.dev/docs/en/knowledgebase/getting-started/) instructions. You can
 also try out one of the [tutorials](https://substrate.dev/en/tutorials).
 
 ## Contributions & Code of Conduct