bump min version to 1.6

Author: simonbyrne

.github/workflows/CI.yml

@@ -14,7 +14,7 @@ jobs:
       matrix:
         version:
           - '1'
-          - '1.5'
+          - '1.6'
           - 'nightly'
         os:
           - ubuntu-latest

Project.toml

@@ -11,7 +11,7 @@ Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"
 
 [compat]
 MPI = "0.14, 0.15, 0.19"
-julia = "1"
+julia = "1.6"
 
 [extras]
 Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"