range.rb: refactor code (use ! instead of not, use favor modifier if and unless usage when having a single-line body)

mrblib/range.rb

@@ -26,9 +26,7 @@ class Range
       return self
     end
 
-    unless val.respond_to? :succ
-      raise TypeError, "can't iterate"
-    end
+    raise TypeError, "can't iterate" unless val.respond_to? :succ
 
     return self if (val <=> last) > 0
 
@@ -37,18 +35,14 @@ class Range
       val = val.succ
     end
 
-    if not exclude_end? and (val <=> last) == 0
-      block.call(val)
-    end
+    block.call(val) if !exclude_end? && (val <=> last) == 0
     self
   end
 
   # redefine #hash 15.3.1.3.15
   def hash
     h = first.hash ^ last.hash
-    if self.exclude_end?
-      h += 1
-    end
+    h += 1 if self.exclude_end?
     h
   end
 end