Update the rbnacl gem to 4.0.2

Gemfile

@@ -396,7 +396,7 @@ gem 'net-ssh', '~> 4.1.0'
 # Required for ED25519 SSH host key support
 group :ed25519 do
   gem 'rbnacl-libsodium'
-  gem 'rbnacl', '~> 3.2'
+  gem 'rbnacl', '~> 4.0'
   gem 'bcrypt_pbkdf', '~> 1.0'
 end

Gemfile.lock

@@ -203,7 +203,7 @@ GEM
       multi_json
     fast_gettext (1.4.0)
     ffaker (2.4.0)
-    ffi (1.9.10)
+    ffi (1.9.18)
     flay (2.8.1)
       erubis (~> 2.7.0)
       path_expander (~> 1.0)
@@ -682,7 +682,7 @@ GEM
     rake (12.0.0)
     rblineprof (0.3.6)
       debugger-ruby_core_source (~> 1.3)
-    rbnacl (3.4.0)
+    rbnacl (4.0.2)
       ffi
     rbnacl-libsodium (1.0.11)
       rbnacl (>= 3.0.1)
@@ -1107,7 +1107,7 @@ DEPENDENCIES
   rainbow (~> 2.2)
   raindrops (~> 0.18)
   rblineprof (~> 0.3.6)
-  rbnacl (~> 3.2)
+  rbnacl (~> 4.0)
   rbnacl-libsodium
   rdoc (~> 4.2)
   re2 (~> 1.1.1)