Fix typo in documentation

bin/duneproject

@@ -627,7 +627,7 @@ INPUT                 += @top_srcdir@/dune/
 #                          @srcdir@/modules
 
 # The EXCLUDE tag can be used to specify files and/or directories that should
-# excluded from the INPUT source files. This way you can easily exclude a
+# be excluded from the INPUT source files. This way you can easily exclude a
 # subdirectory from a directory tree whose root is specified with the INPUT tag.
 
 # EXCLUDE               += @top_srcdir@/dune/$NAME/test