Update image widths in demo section of README

Adjusted image widths in demo links for better layout.

Author: kunitoki

README.md

@@ -6,10 +6,10 @@
 </div>
 
 <div style="display: flex; width: 100%; flex-wrap: nowrap;">
-  <a href="https://kunitoki.github.io/yup/demos/web_render_1/"><img src="./docs/demos/web_render_1.png" style="width:24%;" /></a>
-  <a href="https://kunitoki.github.io/yup/demos/web_render_2/"><img src="./docs/demos/web_render_2.png" style="width:24%;" /></a>
-  <a href="https://kunitoki.github.io/yup/demos/web_render_3/"><img src="./docs/demos/web_render_3.png" style="width:24%;" /></a>
-  <a href="https://kunitoki.github.io/yup/demos/web_render_4/"><img src="./docs/demos/web_render_4.png" style="width:24%;" /></a>
+  <a href="https://kunitoki.github.io/yup/demos/web_render_1/"><img src="./docs/demos/web_render_1.png" style="width:23.5%;" /></a>
+  <a href="https://kunitoki.github.io/yup/demos/web_render_2/"><img src="./docs/demos/web_render_2.png" style="width:23.5%;" /></a>
+  <a href="https://kunitoki.github.io/yup/demos/web_render_3/"><img src="./docs/demos/web_render_3.png" style="width:23.5%;" /></a>
+  <a href="https://kunitoki.github.io/yup/demos/web_render_4/"><img src="./docs/demos/web_render_4.png" style="width:23.5%;" /></a>
 </div>
 
 <div style="display: flex; width: 100%; flex-wrap: nowrap;">