add test for weighted knn
add test for weighted knn

sjwhitworth/golearn,EtienneBruines/golearn,sjwhitworth/golearn,thedadams/golearn,sjwhitworth/golearn,thedadams/golearn,thedadams/golearn,sjwhitworth/golearn,EtienneBruines/golearn,EtienneBruines/golearn,thedadams/golearn,sjwhitworth/golearn