new farmland color - makes farmland less prominent

Currently mapping landuse=farmland in most location results in worse and less readable map for Default map style. Due to massive size it is frequently the most noticeable (or at least one of the most noticeable) features - frequently more prominent than villages or towns. Fixes problem of residential, industrial, farmyard and other landuses not visible enough in sea of landuse=farmland.

distance to landcover closest in color, delta_e94 metric:

hospital/educational area: 4.85
foreground of @bare_ground: 5.02
natural=sand: 5.23
unmapped land: 5.8

closes #1691

landcover.mss

@@ -26,8 +26,8 @@
 @industrial-line: #C6B3C3;  // Lch(75,11,330)
 @railway: @industrial;
 @railway-line: @industrial-line;
-@farmland: #EDDDC9;         // Lch(89,12,80) (Also used for farm)
-@farmland-line: #C8B69E;    // Lch(75,15,80)
+@farmland: #fbecd7;         // Lch(94,12,80) (Also used for farm)
+@farmland-line: #d6c4ab;    // Lch(80,15,80)
 
 @farmyard: #EFD6B5;         // Lch(87,20,80)
 @farmyard-line: #D1B48C;    // Lch(75,25,80)