Updated SageMath version to 8.6

VERSION.txt

-SageMath version 8.6.rc1, Release Date: 2019-01-12
+SageMath version 8.6, Release Date: 2019-01-15

build/pkgs/configure/checksums.ini

 tarball=configure-VERSION.tar.gz
-sha1=f8934cfaf548b23627cb5f0c680e540e4bc3722e
-md5=1e439d981a969e9f6b9811d13fb2c73a
-cksum=1809072073
+sha1=7056135dd3147fad1d6791e1e0389775a434aae0
+md5=5b737189c37f0162cd206badb44beae8
+cksum=3470317803

build/pkgs/configure/package-version.txt

-301
+302

src/bin/sage-version.sh

 # Sage version information for shell scripts
 # This file is auto-generated by the sage-update-version script, do not edit!
-SAGE_VERSION='8.6.rc1'
-SAGE_RELEASE_DATE='2019-01-12'
-SAGE_VERSION_BANNER='SageMath version 8.6.rc1, Release Date: 2019-01-12'
+SAGE_VERSION='8.6'
+SAGE_RELEASE_DATE='2019-01-15'
+SAGE_VERSION_BANNER='SageMath version 8.6, Release Date: 2019-01-15'

src/sage/version.py

 # Sage version information for Python scripts
 # This file is auto-generated by the sage-update-version script, do not edit!
-version = '8.6.rc1'
-date = '2019-01-12'
-banner = 'SageMath version 8.6.rc1, Release Date: 2019-01-12'
+version = '8.6'
+date = '2019-01-15'
+banner = 'SageMath version 8.6, Release Date: 2019-01-15'