Fix #divmod methods

Author: soutaro

core/float.rbs

@@ -442,7 +442,8 @@ class Float < Numeric
   #     13.0.divmod(4.0)            # => [3, 1.0]
   #     13.0.divmod(Rational(4, 1)) # => [3, 1.0]
   #
-  def divmod: (Numeric) -> [ Numeric, Numeric ]
+  def divmod: (Integer | Float | Rational) -> [ Integer, Float ]
+            | (Numeric) -> [ Numeric, Numeric ]
 
   def dup: () -> self
 

core/integer.rbs

@@ -766,7 +766,8 @@ class Integer < Numeric
   #     13.divmod(Rational(4, 1)) # => [3, (1/1)]
   #
   def divmod: (Integer) -> [ Integer, Integer ]
-            | (Float) -> [ Float, Float ]
+            | (Float) -> [ Integer, Float ]
+            | (Rational) -> [ Integer, Rational ]
             | (Numeric) -> [ Numeric, Numeric ]
 
   # <!--

core/rational.rbs

@@ -245,7 +245,8 @@ class Rational < Numeric
 
   def div: (Numeric) -> Integer
 
-  def divmod: (Numeric) -> [ Numeric, Numeric ]
+  def divmod: (Integer | Float | Rational) -> [ Integer, Rational ]
+            | (Numeric) -> [ Numeric, Numeric ]
 
   def dup: () -> self