[gtkmm-documentation/gtkmm-3-22] Don’t write main() without a return type

[Daniel Boles <dboles src gnome org>]

commit 3358cd0b911a76dbbc9a09dffd35239ec4cd5cd9
Author: Daniel Boles <dboles src gmail com>
Date:   Sun Jan 14 20:45:30 2018 +0000

    Don’t write main() without a return type
    
    Yikes! That’s not C++.

 docs/tutorial/C/index-in.docbook |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/docs/tutorial/C/index-in.docbook b/docs/tutorial/C/index-in.docbook
index da0f4a6..04f47a3 100644
--- a/docs/tutorial/C/index-in.docbook
+++ b/docs/tutorial/C/index-in.docbook
@@ -8538,7 +8538,7 @@ void on_button_clicked()
     std::cout &#60;&#60; "Hello World" &#60;&#60; std::endl;
 }
 
-main()
+int main()
 {
     Gtk::Button button("Hello World");
     button.signal_clicked().connect(sigc::ptr_fun(&amp;on_button_clicked));
@@ -8618,7 +8618,7 @@ class some_class
 
 some_class some_object;
 
-main()
+int main()
 {
     Gtk::Button button;
     button.signal_clicked().connect( sigc::ptr_fun(&amp;on_button_clicked) );