tests: use more portable flags in test-fix.t

`head --lines N` is known to not exist on OSX.

Differential Revision: https://phab.mercurial-scm.org/D5517

hgext/fix.py

@@ -62,8 +62,8 b" could use the 'sort' and 'head' utilitie"
 in a text file by ensuring that 'sort' runs before 'head'::
 
   [fix]
-  sort:command = sort --numeric-sort
-  head:command = head --lines=10
+  sort:command = sort -n
+  head:command = head -n 10
   sort:pattern = numbers.txt
   head:pattern = numbers.txt
   sort:priority = 2

tests/test-fix.t

@@ -173,8 +173,8 b' Help text for fix.'
   in a text file by ensuring that 'sort' runs before 'head':
   
     [fix]
-    sort:command = sort --numeric-sort
-    head:command = head --lines=10
+    sort:command = sort -n
+    head:command = head -n 10
     sort:pattern = numbers.txt
     head:pattern = numbers.txt
     sort:priority = 2
@@ -1159,10 +1159,10 b' 5 numbers in the file.'
 
   $ cat >> .hg/hgrc <<EOF
   > [fix]
-  > head:command = head --lines=5
+  > head:command = head -n 5
   > head:pattern = numbers.txt
   > head:priority = 1
-  > sort:command = sort --numeric-sort
+  > sort:command = sort -n
   > sort:pattern = numbers.txt
   > sort:priority = 2
   > EOF