r.mapcalc manual: fix FCELL/float() precision description (fixes https://trac.osgeo.org/grass/ticket/3590)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@72828 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.mapcalc/r.mapcalc.html

@@ -725,7 +725,7 @@ random_int   = rand(-100,100)
 # write result as double precision floating point map (DCELL)
 random_dcell = rand(-100.0,100.0)
 
-# write result as double precision floating point map (FCELL)
+# write result as single precision floating point map (FCELL)
 random_fcell = float(rand(-100.0,100.0))
 </pre></div>