Merge branch 'docs/bump-minimum-go-version' into 'master'

Update doc/update/upgrading_from_source.md

See merge request gitlab-org/gitlab!68759

doc/update/upgrading_from_source.md

@@ -107,11 +107,11 @@ Download and install Go (for Linux, 64-bit):
 # Remove former Go installation folder
 sudo rm -rf /usr/local/go
 
-curl --remote-name --progress "https://dl.google.com/go/go1.13.5.linux-amd64.tar.gz"
-echo '512103d7ad296467814a6e3f635631bd35574cab3369a97a323c9a585ccaa569  go1.13.5.linux-amd64.tar.gz' | shasum -a256 -c - && \
-  sudo tar -C /usr/local -xzf go1.13.5.linux-amd64.tar.gz
+curl --remote-name --progress-bar "https://dl.google.com/go/go1.15.12.linux-amd64.tar.gz"
+echo 'bbdb935699e0b24d90e2451346da76121b2412d30930eabcd80907c230d098b7  go1.15.12.linux-amd64.tar.gz' | shasum -a256 -c - && \
+  sudo tar -C /usr/local -xzf go1.15.12.linux-amd64.tar.gz
 sudo ln -sf /usr/local/go/bin/{go,godoc,gofmt} /usr/local/bin/
-rm go1.13.5.linux-amd64.tar.gz
+rm go1.15.12.linux-amd64.tar.gz
 
 ```