Fix MEMMOVE in rb_darray_insert

Ruby's MEMMOVE takes in the element data type for the third argument, not
the size of the element. What this did was do sizeof(sizeof( ... )) which
always returned sizeof(size_t).

Author: peterzhu2118

darray.h

@@ -58,7 +58,7 @@
     MEMMOVE( \
         rb_darray_ref(*(ptr_to_ary), idx + 1), \
         rb_darray_ref(*(ptr_to_ary), idx), \
-        sizeof((*(ptr_to_ary))->data[0]), \
+        (*(ptr_to_ary))->data[0], \
         rb_darray_size(*(ptr_to_ary)) - idx); \
     rb_darray_set(*(ptr_to_ary), idx, element); \
     (*(ptr_to_ary))->meta.size++; \