use vcs ref in readme

Author: TimMonko

template/README.md.jinja

@@ -13,7 +13,7 @@
 
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-This [napari] plugin was generated with [copier] using the [napari-plugin-template] ({{ _copier_conf.vcs_ref or _copier_conf.src_path or 'development' }}).
+This [napari] plugin was generated with [copier] using the [napari-plugin-template] ({{ _copier_conf.vcs_ref }}).
 
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