Add explicit dependency to mirage-crypto-rng

The old version 0.10.6 fails with

```
File "src/ocamlorg_web/lib/ocamlorg_web.ml", line 12, characters 35-69:
12 |   Mirage_crypto_rng_lwt.initialize (module Mirage_crypto_rng.Fortuna);
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: This expression is packed module, but the expected type is unit
```

So this adds the dependency to the build files as well as to the OPAM
files.

Author: Leonidas-from-XIV

dune-project

@@ -38,6 +38,7 @@
   bos
   crunch
   mirage-kv-mem
+  (mirage-crypto-rng (>= 0.11.0))
   dream-accept
   dream-encoding
   (graphql

ocamlorg.opam

@@ -25,6 +25,7 @@ depends: [
   "bos"
   "crunch"
   "mirage-kv-mem"
+  "mirage-crypto-rng" {>= "0.11.0"}
   "dream-accept"
   "dream-encoding"
   "graphql" {>= "0.14.0"}

src/ocamlorg_web/lib/dune

@@ -10,7 +10,8 @@
   cmarkit
   ocamlorg.data
   timedesc
-  mirage-kv-mem))
+  mirage-kv-mem
+  mirage-crypto-rng))
 
 (rule
  (deps (universe))