Use now mandatory https protocol for MAVEN_CENTRAL

Do so according to [1], which now points to the explanation [2].

Prevently use https also for the gerrit-maven.storage.googleapis.com
domain.

[1] http://repo1.maven.org/maven2/

[2] "Effective January 15, 2020, The Central Repository no longer
supports insecure communication over plain HTTP and requires that all
requests to the repository are encrypted over HTTPS.

If you're receiving this error, then you need to replace all URL
references to Maven Central with their canonical HTTPS counterparts."

Bug: Issue 12170
Change-Id: I001fb42b1a8e97d262cfcffbdb9451094b1b0430
diff --git a/tools/util.py b/tools/util.py
index e8182ed..1d92528 100644
--- a/tools/util.py
+++ b/tools/util.py
@@ -15,9 +15,9 @@
 from os import path
 
 REPO_ROOTS = {
-  'GERRIT': 'http://gerrit-maven.storage.googleapis.com',
+  'GERRIT': 'https://gerrit-maven.storage.googleapis.com',
   'GERRIT_API': 'https://gerrit-api.commondatastorage.googleapis.com/release',
-  'MAVEN_CENTRAL': 'http://repo1.maven.org/maven2',
+  'MAVEN_CENTRAL': 'https://repo1.maven.org/maven2',
   'MAVEN_LOCAL': 'file://' + path.expanduser('~/.m2/repository'),
   'MAVEN_SNAPSHOT': 'https://oss.sonatype.org/content/repositories/snapshots',
 }