% flutter upgrade
Downloading Dart SDK from Flutter engine ae8e6d9f46990b9585dc1fb5b8aabe491c08aaf3...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  120M  100  120M    0     0  4585k      0  0:00:26  0:00:26 --:--:-- 6649k
Building flutter tool...
Got TLS error trying to find package mime at https://pub.dartlang.org.
Error: Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (9 tries left)
Got TLS error trying to find package mime at https://pub.dartlang.org.
Error: Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (8 tries left)

~/flutter % git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
~/flutter % git branch
* master
  stable
~/flutter % git log -1
commit 1cf7b3e2c31462e74eac2a9357f39687fa971e35 (HEAD -> master, origin/master, origin/HEAD)

% cat /etc/os-release 
NAME="Ubuntu"
VERSION="19.04 (Disco Dingo)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 19.04"
VERSION_ID="19.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=disco
UBUNTU_CODENAME=disco

% flutter doctor -v
Building flutter tool...
Got TLS error trying to find package mime at https://pub.dartlang.org.
Error: Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (9 tries left)