fix conversion from Bytes to GigaBytes

When an image with exactly 1MB is used, the fileSizeReadable ouput contains wrong value for file size (instead of 1MB it returns 2MB which is wrong)

src/index.js

@@ -173,14 +173,14 @@ class Files extends React.Component {
   }
 
   fileSizeReadable (size) {
-    if (size >= 1000000000) {
-      return Math.ceil(size / 1000000000) + 'GB'
-    } else if (size >= 1000000) {
-      return Math.ceil(size / 1000000) + 'MB'
-    } else if (size >= 1000) {
-      return Math.ceil(size / 1000) + 'kB'
+    if (size >= 1073741824) {
+        return Math.ceil(size / 1073741824) + 'GB'
+    } else if (size >= 1048576) {
+        return Math.ceil(size / 1048576) + 'MB'
+    } else if (size >= 1024) {
+        return Math.ceil(size / 1024) + 'kB'
     } else {
-      return Math.ceil(size) + 'B'
+        return Math.ceil(size) + 'B'
     }
   }