Fixed scaladoc link to RasterFunctions

Author: metasim

docs/src/main/tut/reference.md

@@ -1,8 +1,8 @@
 # Reference
 
-For the most up to date list of UDFs, look at API documentation for @scaladoc[`ColumnFunctions`][ColumnFunctions]. These UDFs are also registered with the SQL engine under the same name but with a `rf_` prefix (e.g. `dataCells` becomes `rf_dataCells`). 
+For the most up to date list of UDFs, look at API documentation for @scaladoc[`RasterFunctions`][RasterFunctions]. These UDFs are also registered with the SQL engine under the same name but with a `rf_` prefix (e.g. `dataCells` becomes `rf_dataCells`). 
 
 The full API documentation can be found [here][scaladoc].
 
-[ColumnFunctions]: astraea.spark.rasterframes.ColumnFunctions
+[RasterFunctions]: astraea.spark.rasterframes.RasterFunctions
 [scaladoc]: latest/api/index.html