Upgrade to Solr 7.7.3. (#1793)

build.xml

@@ -28,7 +28,7 @@
   <property name="selenium_browser" value="firefox" />
   <property name="snooze_multiplier" value="1" /><!-- can be used to slow down tests (selenium only) -->
   <property name="solr_startup_sleep" value="0" />
-  <property name="solr_version" value="7.4.0" />
+  <property name="solr_version" value="7.7.3" />
   <property name="skip_phpdoc" value="false" />
   <property name="phpdoc_version" value="3.0.0-alpha.4" />
 

config/vufind/searches.ini

@@ -577,7 +577,10 @@ container_title = "Journal Title"
 ; This section allows sharding to be used to pull in content from additional Solr
 ; servers.  All servers used in sharding must contain the same index fields needed
 ; to satisfy queries sent to them AND they must all include different ID numbers!
-; Leave this commented out to disable sharding.
+; Note that additional Solr configuration may also be required; see the "Configuring
+; the ShardHandlerFactory" section of this document for details:
+;    https://lucene.apache.org/solr/guide/7_7/distributed-requests.html
+; Leave this section commented out to disable sharding.
 ; To use sharding, simply fill in lines using the format:
 ; [display name of shard] = [URL of shard (without http://)]
 ;[IndexShards]