Use Unicode in translatable strings

See https://developer.gnome.org/hig/stable/typography.html

https://bugzilla.gnome.org/show_bug.cgi?id=772263

data/appdata/org.gnome.Calendar.appdata.xml.in

@@ -12,7 +12,7 @@
       GNOME Calendar is a simple and beautiful calendar application designed to perfectly fit the GNOME desktop. By reusing the components which the GNOME desktop is build on, Calendar nicely integrates with the GNOME ecosystem.
     </_p>
     <_p>
-      We aim to find the perfect balance between nicely crafted features and user-centred usability. No excess, no lacks. You'll feel comfortable using Calendar, like you've been using it for ages!
+      We aim to find the perfect balance between nicely crafted features and user-centred usability. No excess, no lacks. You’ll feel comfortable using Calendar, like you’ve been using it for ages!
     </_p>
   </description>
 

src/gcal-application.c

@@ -319,7 +319,7 @@ gcal_application_command_line (GApplication            *app,
 
   self = GCAL_APPLICATION (app);
   argv = g_application_command_line_get_arguments (command_line, &argc);
-  context = g_option_context_new (N_("- Calendar management"));
+  context = g_option_context_new (N_("— Calendar management"));
   g_option_context_add_main_entries (context, gcal_application_goptions, GETTEXT_PACKAGE);
 
   error = NULL;