Fix wrong receiver in eoutvar example for #src (#123)

The example was updated to assign the ERB instance to `erb` instead
of `template`, but the following line still called `template.src`.
Since `template` is a String there, the example raises NoMethodError.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: hsbt

lib/erb.rb

@@ -889,7 +889,7 @@ def make_compiler(trim_mode)
   #
   # ```
   # erb = ERB.new(template, eoutvar: '_foo')
-  # puts template.src.split('; ')
+  # puts erb.src.split('; ')
   # #coding:UTF-8
   # _foo = +''
   # _foo.<< "The time is ".freeze