support DataFrames 0.22

Author: mohdibntarek

Project.toml

@@ -12,7 +12,7 @@ NLPModels = "a4795742-8479-5a88-8948-cc11e1c8c1a6"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 
 [compat]
-DataFrames = "^0.20, 0.21"
+DataFrames = "^0.20, 0.21, 0.22"
 JLD2 = "0.1.12, 0.2"
 LinearOperators = "0.4.0, 0.5.0, 0.6.0, 0.7.0, 1.0"
 NLPModels = "0.13"