File rename for consistency

atlas.json

@@ -25,7 +25,7 @@
     "15_payment_requests.asciidoc",
     "16_security_privacy_ln.asciidoc",
     "17_conclusion.asciidoc",
-    "appendix-bitcoin-fundamentals-review.asciidoc",
+    "appendix_bitcoin_fundamentals_review.asciidoc",
     "appendix_docker_basics.asciidoc",
     "appendix_protocol_messages.asciidoc",
     "appendix_license_notices.asciidoc",
@@ -75,4 +75,4 @@
   "lang": "en",
   "accent_color": "",
   "templating": false
-}
+}