fixed a typo in the installation manual

Appendix_A_Installation.ipynb

@@ -324,7 +324,7 @@
     "\n",
     "\n",
     "    sudo apt-get install python3-numpy python3-scipy python3-matplotlib\n",
-    "    sudo apt_get install libblas-dev liblapack-dev gfortran python3-dev \n",
+    "    sudo apt-get install libblas-dev liblapack-dev gfortran python3-dev \n",
     "\n",
     "\n",
     "Now you can upgrade the packages. This will take a long time as everything needs to be compiled from source. If you get an error I do not know how to help you!\n",