Update sicot.f90

tested and works.

source/f90/sicot.f90

@@ -86,14 +86,9 @@ subroutine sicot(f, m, h, x0)
   enddo
 
   j = n
-  do i = 2, n
-    j = j - 1
+  do j = n - 1, 1, -1
     f(j) = f(j) + f(j + 1)
   enddo
-! alternative, but not yet tested:
-!  do j = n - 1, 1, -1
-!    f(j) = f(j) + f(j + 1)
-!  enddo
   msign = -iabs(m)
   call sintr(f, msign, h)
   return