[ruby/resolv] Refine Resolv::LOC::Alt#to_s

Extract the first element instead of `join.to_i` (`String#unpack1` is
available since ruby 2.4.0, but this gem still supports 2.3).

ruby/resolv@f518da95ae

Author: nobu

lib/resolv.rb

@@ -3468,8 +3468,8 @@ def initialize(altitude)
       attr_reader :altitude
 
       def to_s # :nodoc:
-        a = @altitude.unpack("N").join.to_i
-        return ((a.to_f/1e2)-1e5).to_s + "m"
+        a, = @altitude.unpack("N")
+        return "#{(a - Bias).fdiv(100)}m"
       end
 
       def inspect # :nodoc:

test/resolv/test_resource.rb

@@ -95,6 +95,7 @@ def test_alt
     alt = Resolv::LOC::Alt.create(input)
 
     assert_equal([altitude + 1e7].pack("N"), alt.altitude)
+    assert_equal(alt, Resolv::LOC::Alt.create(alt.to_s))
   end
 end