substitute broken link (#1057) (#1058)

use `formulae.brew.sh` as seen in other repositories¹ instead of
`brewformulas.org`, which has been offline since 2020,² to fix #1057.

1. https://github.com/search?type=code&q=/shields.io\/homebrew/+language:reStructuredText
2. https://gitlab.com/zedtux/brewformulas.org/issues/223#note_322019672

Signed-off-by: Lucas Larson <LucasLarson@riseup.net>

Signed-off-by: Lucas Larson <LucasLarson@riseup.net>

docs/installation.rst

@@ -293,7 +293,7 @@ Homebrew
 
 .. image:: https://img.shields.io/homebrew/v/ocrmypdf.svg
     :alt: homebrew
-    :target: http://brewformulas.org/Ocrmypdf
+    :target: https://formulae.brew.sh/formula/ocrmypdf
 
 OCRmyPDF is now a standard `Homebrew <https://brew.sh>`__ formula. To
 install on macOS: