Do not report float numbers as large if fraction has less than 3 digits

spec/ameba/rule/large_numbers_spec.cr

@@ -69,6 +69,10 @@ module Ameba
         11_234e10_f32
         +1.123
         -0.000_5
+
+        1200.0
+        1200.01
+        1200.012
       )
       subject.catch(s).should be_valid
     end

src/ameba/rule/large_numbers.cr

@@ -52,7 +52,7 @@ module Ameba::Rule
     end
 
     private def allowed?(_sign, value, fraction, _suffix)
-      return true unless fraction.nil?
+      return true if !fraction.nil? && fraction.size > 3
 
       digits = value.chars.select &.to_s.=~ /[0-9]/
       digits.size >= int_min_digits