[gnome-calculator/73-in-operator-should-be-localized] Add translator comment (#73)

[Robert Roth <robertroth src gnome org>]

commit bbdeab00616041be06e015ac68c9faf602e2993c
Author: Robert Roth <robert roth off gmail com>
Date:   Thu Sep 6 00:14:28 2018 +0300

    Add translator comment (#73)

 lib/equation-lexer.vala | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/lib/equation-lexer.vala b/lib/equation-lexer.vala
index 4edb4604..61bf356e 100644
--- a/lib/equation-lexer.vala
+++ b/lib/equation-lexer.vala
@@ -692,6 +692,7 @@ public class Lexer : Object
             return insert_token (LexerTokenType.XOR);
         if (name == "not")
             return insert_token (LexerTokenType.NOT);
+        // Translators: conversion keyword, used e.g. 1 EUR in USD
         if (name == _("in"))
             return insert_token (LexerTokenType.IN);
         if (check_if_function ())