[epiphany] Fix typo in HACKING file

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 894dd409d1d52bacb4b04ba1d4f59563d963ddd8
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Tue Feb 21 11:05:35 2017 -0600

    Fix typo in HACKING file

 HACKING |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/HACKING b/HACKING
index 05d7e48..a397d47 100644
--- a/HACKING
+++ b/HACKING
@@ -72,7 +72,7 @@ you go out of your way to do so.
 GTK APPLICATION AND EPHY SHELL
 ==============================
 
-Epiphany has one singleton EphyShell object. Its inheritance heirarchy is:
+Epiphany has one singleton EphyShell object. Its inheritance hierarchy is:
 
  - GApplication
  --- GtkApplication