patch 8.2.0532: cannot use simplify() as a method

Problem:    Cannot use simplify() as a method.
Solution:   Add FEARG_1. (closes #5996)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 40fb9e9..7170c0e 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -837,7 +837,7 @@
     {"sign_undefine",	0, 1, FEARG_1,	  ret_number,	SIGN_FUNC(f_sign_undefine)},
     {"sign_unplace",	1, 2, FEARG_1,	  ret_number,	SIGN_FUNC(f_sign_unplace)},
     {"sign_unplacelist", 1, 2, FEARG_1,	  ret_list_number, SIGN_FUNC(f_sign_unplacelist)},
-    {"simplify",	1, 1, 0,	  ret_string,	f_simplify},
+    {"simplify",	1, 1, FEARG_1,	  ret_string,	f_simplify},
     {"sin",		1, 1, FEARG_1,	  ret_float,	FLOAT_FUNC(f_sin)},
     {"sinh",		1, 1, FEARG_1,	  ret_float,	FLOAT_FUNC(f_sinh)},
     {"sort",		1, 3, FEARG_1,	  ret_list_any,	f_sort},