bpo-36546: Mark first argument as position only (GH-14363)

diff --git a/Lib/statistics.py b/Lib/statistics.py
index 5be70e5..79b65a2 100644
--- a/Lib/statistics.py
+++ b/Lib/statistics.py
@@ -603,7 +603,7 @@
 # options make for easier choices and that external packages can be
 # used for anything more advanced.
 
-def quantiles(dist, *, n=4, method='exclusive'):
+def quantiles(dist, /, *, n=4, method='exclusive'):
     '''Divide *dist* into *n* continuous intervals with equal probability.
 
     Returns a list of (n - 1) cut points separating the intervals.