Do not allocate memory useless

Author: greenbigfrog

src/pg_ext/big_decimal.cr

@@ -4,7 +4,7 @@ module PG
   struct Numeric
     # Returns a BigDecimal representation of the numeric. This retains all precision.
     def to_big_d
-      return BigDecimal.new("0") if nan? || ndigits == 0
+      return BigDecimal.new(0) if nan? || ndigits == 0
       BigDecimal.new(to_s)
     end
   end