Use latest version of rand

Author: iquerejeta

Cargo.lock

@@ -26,7 +26,6 @@ digest      = { version = "0.10.5", features = ["alloc"] }
 num-bigint  = { version = "0.4.0", optional = true }
 num-rational = { version = "0.4.0", optional = true }
 num-traits  = { version = "0.2.14", optional = true }
-rand = "0.6.1"
 rand_core   = "0.6.3"
 rayon       = "1.5.1"
 rug = { version = "1.14", optional = true }
@@ -40,6 +39,7 @@ hex = "0.4.3"
 num-bigint  = "0.4.0"
 num-rational = "0.4.0"
 proptest    = "1.0.0"
+rand = "0.8"
 rand_chacha = "0.3.1"
 
 [[bench]]