package/fetchmail: bump version to 6.4.0.rc1

Updated license hash after upstream commit:
https://sourceforge.net/p/fetchmail/git/ci/c58fae843fbcbd3c1040a7fbc2196fbc758cc186/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/fetchmail/fetchmail.hash

@@ -1,3 +1,3 @@
 # Locally computed:
-sha256 832fded80908670d0ae31b4ac4a4e292d4fdb1855578bb9ac0e9e2f63efa5a39  fetchmail-6.4.0.beta5.tar.xz
-sha256 8b9e9688c0fc566adfa56f9d9ebaabf60e5a58ca365a282cf5742bd22fd97378  COPYING
+sha256 8b6c7c113b58ca32b3041375bdab4b2e4e6e98c975e1365de5e51f63ef07bf2e  fetchmail-6.4.0.rc1.tar.xz
+sha256 678189d91119286a3499874421006bb81f49b13eff8e1223115ce1b07e7ed0e7  COPYING

package/fetchmail/fetchmail.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 FETCHMAIL_VERSION_MAJOR = 6.4
-FETCHMAIL_VERSION = $(FETCHMAIL_VERSION_MAJOR).0.beta5
+FETCHMAIL_VERSION = $(FETCHMAIL_VERSION_MAJOR).0.rc1
 FETCHMAIL_SOURCE = fetchmail-$(FETCHMAIL_VERSION).tar.xz
 FETCHMAIL_SITE = http://downloads.sourceforge.net/project/fetchmail/branch_$(FETCHMAIL_VERSION_MAJOR)
 FETCHMAIL_LICENSE = GPL-2.0; some exceptions are mentioned in COPYING