fix typo

Author: jvdp1

doc/specs/stdlib_sorting.md

@@ -211,7 +211,7 @@ increasing, or decreasing, value.
 
 ##### Syntax
 
-`call [[stdlib_sorting(module):ord_sort(subroutine)]]ord_sort ( array[, work, reverse ] )`
+`call [[stdlib_sorting(module):ord_sort(interface)]]( array[, work, reverse ] )`
 
 ##### Class
 
@@ -286,7 +286,7 @@ decreasing, value.
 
 ##### Syntax
 
-`call [[stdlib_sorting(module):sort(subroutine)]]sort ( array[, reverse] )`
+`call [[stdlib_sorting(module):sort(interface)]]( array[, reverse] )`
 
 ##### Class
 
@@ -349,7 +349,7 @@ sort the input `array` to produce the output `array`.
 
 ##### Syntax
 
-`call [[stdlib_sorting(module):sort_index(subroutine)]]sort_index ( array, index[, work, iwork, reverse ] )`
+`call [[stdlib_sorting(module):sort_index(interface)]]( array, index[, work, iwork, reverse ] )`
 
 ##### Class