fix off-by-one error in isolating raw frontmatter

src/index.ts

@@ -42,7 +42,7 @@ export default function gemtext(config: GemtextConfig = {}): AstroIntegration {
 
                       if (lines.at(0) === '---' && lines.lastIndexOf('---') > 0) {
                         bodyStartLineIndex = lines.indexOf('---', 1) + 1;
-                        frontmatter = lines.slice(1, bodyStartLineIndex).join('\n');
+                        frontmatter = lines.slice(1, bodyStartLineIndex - 1).join('\n');
                         try {
                           data = { ...data, ...parseYaml(frontmatter, { schema: 'yaml-1.1' }) };
                         } catch { }