Replace emoji with Greek letters in Unicode string example

The emoji characters (U+1F60E) rendered as empty squares in the PDF
because they are outside the Noto Serif font coverage. Replaced with
Greek letters lambda, pi, sigma (955, 960, 963) which Noto Serif
supports and which still demonstrate the +pc unicode shell behavior.

Fixes #211

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: happi

chapters/type_system.asciidoc

@@ -389,25 +389,25 @@ defaults to the Latin-1 range when detecting strings, so for example:
 
 [source,erlang]
 ----
-2> [128526, 128526, 128526].
-[128526, 128526, 128526]
+2> [955, 960, 963].
+[955,960,963]
 ----
 
-just shows the result as a list of numbers. However, if we start Erlang
+just shows the result as a list of numbers, even though 955, 960, and 963
+are the Greek letters lambda, pi, and sigma. However, if we start Erlang
 with the option `+pc unicode`, the Erlang shell will be much more generous
 with what it considers printable:
 
 [source,shell]
 ----
-Eshell V15.2.2 (press Ctrl+G to abort, type help(). for help)
 $ erl +pc unicode
 Erlang/OTP 27 [erts-15.2.2] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]
 
 Eshell V15.2.2 (press Ctrl+G to abort, type help(). for help)
-1> [128526, 128526, 128526].
-"😎😎😎"
-2> 
+1> [955, 960, 963].
+"λπσ"
 ----
+
 Just note that it depends on your console, what encoding it is set to
 expect, and its available fonts, whether it will be able to actually
 display those characters.