fixed the browser refreshing when the encode/decode button is pressed on base64

tools/Base64/index.html

@@ -2,8 +2,8 @@
 <form>
     <label>Input data</label>
     <textarea value="" rows="3" id="input" required></textarea>
-    <button onclick="doencode();">Encode</button>
-    <button onclick="dodecode();">Decode</button>
+    <button type="button" onclick="doencode();">Encode</button>
+    <button type="button" onclick="dodecode();">Decode</button>
     <label>Output</label>
     <textarea id="output" disabled></textarea>
 </form>