fixed exercise bug in 006

Author: giumas

006_Read_and_Write_Text_Files.ipynb

@@ -659,7 +659,7 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "solution2": "shown",
+    "solution2": "hidden",
     "solution2_first": true
    },
    "source": [
@@ -672,7 +672,7 @@
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
-    "solution2": "shown"
+    "solution2": "hidden"
    },
    "outputs": [],
    "source": [