Fix ENV.update implementation.

Author: bjfish

CHANGELOG.md

@@ -65,6 +65,7 @@ Bug fixes:
 * Removed "shadowing outer local variable" warning.
 * Fixed parameter conversion to `String` in ENV methods.
 * Fixed deprecation warning when `ENV.index` is called.
+* Fixed `ENV.udpate` implementation.
 
 Compatibility:
 

spec/tags/core/env/update_tags.txt

@@ -284,11 +284,14 @@ def to_h
   end
 
   def update(other)
+    return self if equal?(other)
+    other = Truffle::Type.rb_convert_type(other, Hash, :to_hash)
     if block_given?
       other.each { |k, v| self[k] = yield(k, lookup(k), v) }
     else
       other.each { |k, v| self[k] = v }
     end
+    self
   end
 
   def keep_if(&block)