Rename 'npm run upgrade' to 'npm run upgrade-peertube'

It was confusing with the command 'npm run update'

scripts/upgrade.sh

@@ -1,31 +0,0 @@
-#!/bin/bash
-
-nodeMinVersion="v6.0.0"
-npmMinVersion="3.0.0"
-
-if [[ $(node --version) < $nodeMinVersion ]]; then
-  echo 'You need node >= 6'
-  exit 0
-fi
-
-if [[ $(npm --version) < $npmMinVersion ]]; then
-  echo 'You need npm >= 3'
-  exit 0
-fi
-
-if ! which yarn > /dev/null; then
-  echo 'You need yarn'
-  exit 0
-fi
-
-if pgrep peertube > /dev/null; then
-  echo 'PeerTube is running!'
-  exit 0
-fi
-
-git pull origin $(git rev-parse --abbrev-ref HEAD) || exit -1
-
-yarn install --pure-lockfile
-npm run build
-
-echo "\n\nUpgrade finished! You can restart PeerTube that may run the migration scripts."