style: replace dfg logo and make it clickable

src/.vuepress/components/Footer.vue

@@ -47,12 +47,14 @@
     <v-col
       cols="12"
     >
-      <v-img
-        max-height="100%"
-        max-width="200px"
-        style="margin: 0 auto"
-        :src="$withBase('/assets/images/dfg_logo_schriftzug_blau_foerderung_en.svg')"
-        ></v-img>
+      <a href="https://www.dfg.de/" target="_blank">
+        <v-img
+          max-height="100%"
+          max-width="200px"
+          style="margin: 0 auto"
+          :src="$withBase('/assets/images/dfg_logo_schriftzug_weiss.svg')"
+          ></v-img>
+      </a>
     </v-col>
     <v-col
       class="text-caption grey--text text--lighten-3 text-center copyright"