Update analysis_notebook_hashtag.ipynb

Fix of date time transformation for date specific filtering.

analysis_notebook_hashtag.ipynb

@@ -89,7 +89,7 @@
    "source": [
     "# Changes 'created_at' to data format datetime64[ns, tzlocal()]\n",
     "# That is necessary for date specific filtering\n",
-    "df['created_at'] = pd.to_datetime(df['created_at'], utc=True)\n",
+    "df['created_at'] = pd.to_datetime(df['created_at'], errors='coerce',  utc=True)\n",
     "\n",
     "# Adding the column 'instance' by extracting the domain name (and suffix) from the column 'url' of the post\n",
     "df['instance'] = df['url'].apply(lambda x: urlparse(x)[1])"