docs: ensure pip is up to date

Signed-off-by: Carlos A Becker <caarlos0@users.noreply.github.com>

scripts/vercel/install.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
 set -euo pipefail
 yum install -y jq
+pip install --upgrade pip
 pip install mkdocs-material mkdocs-redirects mkdocs-minify-plugin lunr