docs: Fix syntax-check error

commit id '40cb5581' caused syntax-check error:

prohibit_empty_lines_at_EOF
docs/manifest.json
maint.mk: empty line(s) or no newline at EOF
maint.mk:929: recipe for target 'sc_prohibit_empty_lines_at_EOF' failed
make: *** [sc_prohibit_empty_lines_at_EOF] Error 1

I just edited the file and replaced the closing } and it made things happy

docs/manifest.json

@@ -15,4 +15,4 @@
     "theme_color": "#ffffff",
     "background_color": "#ffffff",
     "display": "standalone"
-}
+}
\ No newline at end of file