Fix mongoose docs generation

PUBLISHED_FROM=331821dcd1f7dc8a94581cd8a9b51aa00a89fddc

docs/c-api/mg_util.h/mg_basic_auth_header.md

@@ -0,0 +1,13 @@
+---
+title: "mg_basic_auth_header()"
+decl_name: "mg_basic_auth_header"
+symbol_kind: "func"
+signature: |
+  void mg_basic_auth_header(const struct mg_str user, const struct mg_str pass,
+                            struct mbuf *buf);
+---
+
+Generate a Basic Auth header and appends it to buf.
+If pass is NULL, then user is expected to contain the credentials pair
+already encoded as `user:pass`. 
+