Fix grammatical error (#40)

diff --git a/ b/
index 7d75d40..1adaeea 100644
--- a/
+++ b/
@@ -39,7 +39,7 @@
 because string operations are not working at the grapheme cluster level.
 For example, to abbreviate a text to, say, the 15 first characters or glyphs,
-an string like "A 🇬🇧 text in English"
+a string like "A 🇬🇧 text in English"
 should abbreviate to "A 🇬🇧 text in Eng… when counting characters,
 but will become "A 🇬🇧 text in …"
 if counting code units using [`String`][String] operations.