Return vector instead of dict in spectralindices

Author: juliohm

src/transforms/spectralindex.jl

@@ -100,7 +100,7 @@ end
 
 List of spectral indices supported by SpectralIndices.jl.
 """
-spectralindices() = indices
+spectralindices() = collect(values(indices))
 
 """
     spectralbands(name)

test/transforms/spectralindex.jl

@@ -36,6 +36,6 @@
   @test T(t).NDVI ≈ [0.6, 0.42857142857142855, 0.3333333333333333]
 
   # auxiliary functions
-  @test spectralindices() isa Dict
+  @test spectralindices() isa Vector
   @test spectralbands("NDVI") isa Vector
 end