Allow JSON v0.21 and bump version to 5.1.3. (#149)

Author: fredrikekre

Project.toml

@@ -1,6 +1,6 @@
 name = "GitHub"
 uuid = "bc5e4493-9b4d-5f90-b8aa-2b2bcaad7a26"
-version = "5.1.2"
+version = "5.1.3"
 
 [deps]
 Base64 = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"
@@ -12,7 +12,7 @@ Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"
 
 [compat]
 HTTP = "0.8"
-JSON = "0.19, 0.20"
+JSON = "0.19, 0.20, 0.21"
 MbedTLS = "0.6, 0.7"
 julia = "0.7, 1"