Use HREF url to extract list of releases from erlang.org

Kerl previously used the contents of the HTML <a> tag for this purpose.  Unfortunately,
the HTML <a> tag is not always rendered as expected.

The old output from "kerl update releases":
------
Getting the available releases from erlang.org...
The available releases are:
R10B-0 R10B-2 R10B-3 R10B-4 R10B-5 R10B-6 R10B-7 R10B-8 R10B-9 R11B-0 R11B-1 R11B-2 R11B-3 R11B-4 R11B-5 R12B-0 R12B-1 R12B-2 R12B-3 R12B-4 R12B-5 R13A R13B R13B01 R13B02 R13B03 R13B04 R14A R14B R14B01 R14B02 R14B03 R14B04 R15B R15B01 R15B02 R15B03
------

The new output from "kerl update releases":
------
Getting the available releases from erlang.org...
The available releases are:
R10B-0 R10B-10 R10B-2 R10B-3 R10B-4 R10B-5 R10B-6 R10B-7 R10B-8 R10B-9 R11B-0 R11B-1 R11B-2 R11B-3 R11B-4 R11B-5 R12B-0 R12B-1 R12B-2 R12B-3 R12B-4 R12B-5 R13A R13B R13B01 R13B02-1 R13B02 R13B03 R13B04 R14A R14B R14B01 R14B02 R14B03 R14B04 R15B R15B01 R15B02 R15B03-1 R15B03
------

1 files changed, 1 insertions, 1 deletions

diff --git a/kerl b/kerl
index 43220d6..d50f7c5 100755
--- a/kerl
+++ b/kerl
@@ -114,7 +114,7 @@ if [ $# -eq 0 ]; then usage; fi
 get_releases()
 {
     curl -s $ERLANG_DOWNLOAD_URL/ | \
-        sed $SED_OPT -e 's/^.*>otp_src_(R1[-1234567890ABCD]+)\.tar\.gz<.*$/\1/' \
+        sed $SED_OPT -e 's/^.*<[aA] [hH][rR][eE][fF]=\"\/download\/otp_src_(R1[-1234567890ABCD]+)\.tar\.gz\">.*$/\1/' \
                      -e '/^R/!d'
 }