fixed extension of pictures

Author: graydonli

docs/en/product_documents/m5stack-core/m5go_iot_starter_kit.md

@@ -158,19 +158,19 @@ We also supply some courses for teaching IOT programming. If you are interesting
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/m5go/m5go_02.jpg" width="500">
+    <img src="assets/img/product_pics/core/m5go/m5go_02.png" width="500">
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/m5go/m5go_03.jpg" width="500">
+    <img src="assets/img/product_pics/core/m5go/m5go_03.png" width="500">
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/m5go/m5go_04.jpg" width="500">
+    <img src="assets/img/product_pics/core/m5go/m5go_04.png" width="500">
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/m5go/m5go_05.jpg" width="500">
+    <img src="assets/img/product_pics/core/m5go/m5go_05.png" width="500">
 </figure>
 
 <figure>

docs/en/product_documents/m5stack-core/minicore_stick.md

@@ -66,13 +66,13 @@ MPU9250 Version:
 -  **<mark>Quick Start</mark>** - [Arduino](en/quick_start/m5core/m5stick_get_started_arduino)
 
 <figure>
-    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_01.jpg" height="500" width="500">
+    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_01.png" height="500" width="500">
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_02.jpg" height="500" width="500">
+    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_02.png" height="500" width="500">
 </figure>
 
 <figure>
-    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_03.jpg" height="500" width="500">
+    <img src="assets/img/product_pics/core/minicore/m5stick/m5stick_03.png" height="500" width="500">
 </figure>