restricted DataFrames versions

Author: MariaHei

Project.toml

@@ -27,7 +27,7 @@ SuiteSparse = "4607b0f0-06f3-5cda-b6b1-a6196a1729e9"
 BenchmarkTools = "1.0 - 1.5"
 BSON = "0.3"
 CSV = "0.10"
-DataFrames = "0.21 - 1.6"
+DataFrames = "1.6"
 DataStructures = "0.18"
 Distributions = "0.23 - 0.25"
 Documenter = "0.25 - 0.27"