Updated SageMath version to 8.7.rc0

VERSION.txt

-SageMath version 8.6, Release Date: 2019-01-15
+SageMath version 8.7.rc0, Release Date: 2019-01-23

build/pkgs/configure/checksums.ini

 tarball=configure-VERSION.tar.gz
-sha1=7056135dd3147fad1d6791e1e0389775a434aae0
-md5=5b737189c37f0162cd206badb44beae8
-cksum=3470317803
+sha1=eddb6967bb5ceb7c5c50e5d519e1e16d6221c278
+md5=eb53690e6c06ca1901d8ac425e8488fa
+cksum=1943747897

build/pkgs/configure/package-version.txt

-302
+303

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'
-SAGE_RELEASE_DATE='2019-01-15'
-SAGE_VERSION_BANNER='SageMath version 8.6, Release Date: 2019-01-15'
+SAGE_VERSION='8.7.rc0'
+SAGE_RELEASE_DATE='2019-01-23'
+SAGE_VERSION_BANNER='SageMath version 8.7.rc0, Release Date: 2019-01-23'

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'
-date = '2019-01-15'
-banner = 'SageMath version 8.6, Release Date: 2019-01-15'
+version = '8.7.rc0'
+date = '2019-01-23'
+banner = 'SageMath version 8.7.rc0, Release Date: 2019-01-23'