Update install_erpnext.py

Update is_redhat variable becose distribution response with "red hat enterprise linux server" and response is False.
diff --git a/install_erpnext.py b/install_erpnext.py
index 303c83b..da8dc06 100644
--- a/install_erpnext.py
+++ b/install_erpnext.py
@@ -72,7 +72,7 @@
 	# check distribution
 	distribution = platform.linux_distribution()[0].lower().replace('"', '')
 	print "Distribution = ", distribution
-	is_redhat = distribution in ("redhat", "centos", "centos linux", "fedora")
+	is_redhat = distribution in ("redhat", "red hat enterprise linux server", "centos", "centos linux", "fedora")
 	is_debian = distribution in ("debian", "ubuntu", "elementary os", "linuxmint")
 	
 	if not (is_redhat or is_debian):