Clarify Emacs 27+ requiement

Author: dgutov

.github/workflows/ci.yml

@@ -25,8 +25,6 @@ jobs:
       fail-fast: false
       matrix:
         emacs_version:
-          - '26.1'
-          - '26.3'
           - '27.2'
           - '28.2'
           - '29.4'

README.md

@@ -66,7 +66,7 @@ diff-hl-margin-mode
 Requirements
 =====
 
-Emacs 26.1+.
+Emacs 27.1+.
 
 Notes
 =====

diff-hl.el

@@ -1758,7 +1758,7 @@ effect."
       (message "Showing changes against %s (project %s)" rev name)))))
 
 (defun diff-hl--project-root (proj)
-  ;; Emacs 26 and 27 don't have `project-root'.
+  ;; Emacs 27 does not have `project-root'.
   (expand-file-name (static-if (>= emacs-major-version 28)
                         (project-root proj)
                       (project-roots proj))))