updated notebooks to phiflow 3.1

diffphys-code-burgers.ipynb

@@ -32,7 +32,7 @@
    },
    "outputs": [],
    "source": [
-    "!pip install --upgrade --quiet phiflow==2.2\n",
+    "!pip install --upgrade --quiet phiflow==3.1\n",
     "from phi.tf.flow import *\n",
     "\n",
     "N = 128\n",

diffphys-code-ns.ipynb

@@ -86,7 +86,7 @@
    },
    "outputs": [],
    "source": [
-    "!pip install --upgrade --quiet phiflow==2.2\n",
+    "!pip install --upgrade --quiet phiflow==3.1\n",
     "from phi.torch.flow import *  \n",
     "import pylab # for visualizations later on"
    ]

overview-burgers-forw.ipynb

@@ -45,12 +45,12 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Using phiflow version: 2.2.0\n"
+      "Using phiflow version: 3.1.0\n"
      ]
     }
    ],
    "source": [
-    "!pip install --upgrade --quiet phiflow==2.2\n",
+    "!pip install --upgrade --quiet phiflow==3.1\n",
     "from phi.flow import *\n",
     "\n",
     "from phi import __version__\n",