bump nlpmodels 0.19 (#51)

Author: tmigot

Project.toml

@@ -10,7 +10,7 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [compat]
-NLPModels = "0.18"
+NLPModels = "0.18, 0.19"
 NLPModelsModifiers = "0.6"
 julia = "^1.3.0"