Update rdoc to remove some warnings

Author: nbudin

Gemfile.lock

@@ -187,7 +187,7 @@ GEM
     crass (1.0.6)
     csv (3.3.5)
     dalli (3.2.8)
-    date (3.4.1)
+    date (3.5.0)
     dead_end (4.0.0)
     debug (1.11.0)
       irb (~> 1.10)
@@ -240,7 +240,7 @@ GEM
       dotenv (= 3.1.8)
       railties (>= 6.1)
     drb (2.2.3)
-    erb (5.0.3)
+    erb (5.1.3)
     erubi (1.13.1)
     erubis (2.7.0)
     eu_central_bank (1.7.0)
@@ -502,9 +502,10 @@ GEM
       msgpack (>= 0.4.3)
       optimist (>= 3.0.0)
     rbtree (0.4.6)
-    rdoc (6.14.2)
+    rdoc (6.15.1)
       erb
       psych (>= 4.0.0)
+      tsort
     recaptcha (5.21.1)
     redcarpet (3.6.1)
     regexp_parser (2.11.3)