Fix IPA builder version typo

Fix typo of the IPA builder version variable name

Change-Id: If858d57d820d1221759acf8ab3f0478522c68c88
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>

etc/kayobe/ipa.yml

@@ -17,7 +17,7 @@
 #ipa_builder_source_url:
 
 # Version of IPA builder source repository. Default is master.
-#ipa_build_source_version:
+#ipa_builder_source_version:
 
 # List of default Diskimage Builder (DIB) elements to use when building IPA
 # images. Default is ["centos", "enable-serial-console",