Update xpdfreader package installation (#2491)

This Update will fix this exception `Exception: pdftotext is not installed. It is part of xpdf or poppler-utils software suite. ` Now, converting PDFs wouldn't have any issues.

tutorials/Tutorial16_Document_Classifier_at_Index_Time.ipynb

@@ -46,10 +46,10 @@
     "\n",
     "# Install the latest master of Haystack\n",
     "!pip install --upgrade pip\n",
-    "!pip install git+https://github.com/deepset-ai/haystack.git#egg=farm-haystack[colab, ocr]\n",
+    "!pip install git+https://github.com/deepset-ai/haystack.git#egg=farm-haystack[colab,ocr]\n",
     "\n",
-    "!wget --no-check-certificate https://dl.xpdfreader.com/xpdf-tools-linux-4.03.tar.gz\n",
-    "!tar -xvf xpdf-tools-linux-4.03.tar.gz && sudo cp xpdf-tools-linux-4.03/bin64/pdftotext /usr/local/bin\n",
+    "!wget --no-check-certificate https://dl.xpdfreader.com/xpdf-tools-linux-4.04.tar.gz\n",
+    "!tar -xvf xpdf-tools-linux-4.04.tar.gz && sudo cp xpdf-tools-linux-4.04/bin64/pdftotext /usr/local/bin\n",
     "\n",
     "# Install  pygraphviz\n",
     "!apt install libgraphviz-dev\n",
@@ -534,4 +534,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 2
-}
+}