Add safe navigation operator to handle case when proxy key exists but…

… has a value of 'nil'

lib/excon/utils.rb

@@ -50,7 +50,7 @@ def redact(datum)
       if datum.has_key?(:password)
         datum[:password] = REDACTED
       end
-      if datum.has_key?(:proxy) && datum[:proxy].has_key?(:password)
+      if datum.has_key?(:proxy) && datum[:proxy]&.has_key?(:password)
         datum[:proxy] = datum[:proxy].dup
         datum[:proxy][:password] = REDACTED
       end