Increase contrast between waterways and ski pistes

we can do:
- waterways are more on the green/teal side of blue,
- pistes are more on the red/magenta side of blue

css/50_misc.css

@@ -93,7 +93,7 @@ path.line.casing.tag-aerialway {
 
 /* pistes */
 path.line.stroke.tag-piste {
-    stroke: #9ac;
+    stroke: #a9d;
 }
 path.line.casing.tag-piste {
     stroke: #444;