Avoid non-ASCII characters in help text

doc/bufexplorer.txt

@@ -510,7 +510,7 @@ CHANGE LOG                                              *bufexplorer-changelog*
     - Dave Eggum has made some 'significant' updates to this latest
       version:
       * Added BufExplorerGetAltBuf() global function to be used in the
-        user’s rulerformat.
+        user's rulerformat.
       * Added g:bufExplorerSplitRight option.
       * Added g:bufExplorerShowRelativePath option with mapping.
       * Added current line highlighting.