EnvironmentDialog: Add missing full stop

Change-Id: I90905985650c957ab6ae648ecf8baa92deb865a7
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

src/libs/utils/environmentdialog.cpp

@@ -48,7 +48,7 @@ Utils::optional<EnvironmentItems> EnvironmentDialog::getEnvironmentItems(
            "To set or change a variable, use VARIABLE=VALUE.\n"
            "Existing variables can be referenced in a VALUE with ${OTHER}.\n"
            "To clear a variable, put its name on a line with nothing else on it.\n"
-           "To disable a variable, prefix the line with \"#\""));
+           "To disable a variable, prefix the line with \"#\"."));
 }
 
 } // namespace Utils