[emacs] fix magit-blame-mode

Wrap magit-blame in its own use-package declaration so it gets loaded
properly when magit-blame-mode is run.

.emacs.d/emacs.org

@@ -90,8 +90,7 @@
        :commands (magit-init
                   magit-status
                   magit-diff
-                  magit-commit
-                  magit-blame-mode)
+                  magit-commit)
        :config
        (progn
          (defadvice magit-status (around magit-fullscreen activate)
@@ -102,6 +101,10 @@
          (defadvice magit-quit-window (around magit-restore-screen activate)
            ad-do-it
            (jump-to-register :magit-fullscreen))))
+
+     (use-package magit-blame
+       :ensure magit
+       :commands (magit-blame-mode))
    #+END_SRC
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