I installed from scratch this morning and it says it is already 8.1:
Flarum core 0.1.0-beta.8.1
PHP version: 7.1.24
Loaded extensions: Core, date, libxml, openssl, pcre, zlib, filter, hash, pcntl, readline, Reflection, SPL, session, standard, bcmath, bz2, calendar, ctype, curl, dom, mbstring, fileinfo, ftp, gd, gettext, iconv, json, exif, mysqlnd, PDO, Phar, posix, shmop, SimpleXML, sockets, sqlite3, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xml, xmlwriter, xsl, mysqli, pdo_mysql, pdo_sqlite, wddx, xmlreader, zip, Zend OPcache
+----------------------+-----------------+--------+
| Flarum Extensions | | |
+----------------------+-----------------+--------+
| ID | Version | Commit |
+----------------------+-----------------+--------+
| flarum-approval | v0.1.0-beta.8 | |
| flarum-bbcode | v0.1.0-beta.8 | |
| flarum-emoji | v0.1.0-beta.8 | |
| flarum-flags | v0.1.0-beta.8.1 | |
| flarum-likes | v0.1.0-beta.8.1 | |
| flarum-lock | v0.1.0-beta.8 | |
| flarum-markdown | v0.1.0-beta.8 | |
| flarum-mentions | v0.1.0-beta.8.1 | |
| flarum-sticky | v0.1.0-beta.8 | |
| flarum-subscriptions | v0.1.0-beta.8 | |
| flarum-suspend | v0.1.0-beta.8 | |
| flarum-tags | v0.1.0-beta.8.2 | |
| flarum-lang-english | v0.1.0-beta.8 | |
| flarum-statistics | v0.1.0-beta.8 | |
+----------------------+-----------------+--------+