Update sponsor SVG assets

Author: nikoscham

assets/Sponsor_GitHub.svg

@@ -139,9 +139,7 @@ <h1 class="top">
         src="./assets/cold-plate-logo-results.png"
         alt="Results of heat conduction around the FEAScript logo"
       />
-      <p class="image-caption">
-        Heat conduction around the FEAScript logo
-      </p>
+      <p class="image-caption">Heat conduction around the FEAScript logo</p>
       <img
         src="./assets/advection-diffusion-1d-results.png"
         alt="Results of advection-diffusion with Gaussian source tutorial"
@@ -356,16 +354,12 @@ <h2 id="howtousefeascript"><a name="Getting Started"></a>How to Use FEAScript</h
         donation:</strong
       >
       <a href="https://github.com/sponsors/FEAScript" class="sponsor-link">
-        <img
-          alt="GitHub Sponsors"
-          src="https://img.shields.io/static/v1?label=Sponsor&message=%E2%9D%A4&logo=GitHub&color=%23fe8e86"
-          style="vertical-align: middle"
-        />
+        <img alt="GitHub Sponsors" src="./assets/Sponsor_GitHub.svg" style="vertical-align: middle" />
       </a>
       <a href="https://liberapay.com/FEAScript/donate" class="sponsor-link">
         <img
           alt="Donate using Liberapay"
-          src="https://img.shields.io/badge/Liberapay-F6C915?logo=liberapay&logoColor=black"
+          src="./assets/Sponsor_Liberapay.svg"
           style="vertical-align: middle"
         />
       </a>