examples env: add upper version constraint for numpy to keep compatibility with python3.5

examples/Pipfile

@@ -13,6 +13,8 @@ notebook = "*"
 ipython = "<7.10.0"
 # https://github.com/jupyter/nbconvert/commit/e87b847b23e1ae56461f7a7b7d54c44285ce91f1#diff-60f61ab7a8d1910d86d9fda2261620314edcae5894d5aaa236b821c7256badd7L192
 nbconvert = "<6"
+# https://github.com/numpy/numpy/commit/fbcb58ca2c17217f5dc85cb669ea651b7799b60c#diff-60f61ab7a8d1910d86d9fda2261620314edcae5894d5aaa236b821c7256badd7R30
+numpy = "<1.19"
 # https://github.com/ipython/traitlets/commit/8c2554364bd80af917aff1a7725a967ab1203fed
 traitlets = "<5"
 

examples/Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "fab57e995d6e99e3ddaaa1d6573c637ee8c7fd439751f48d5eb0d47cc737d371"
+            "sha256": "2bcc75b7ce44603c5856542cbe40059c600fe3281b2c7d9ce1503b955e7b0b51"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -296,6 +296,7 @@
                 "sha256:ef627986941b5edd1ed74ba89ca43196ed197f1a206a3f18cc9faf2fb84fd675",
                 "sha256:f718a7949d1c4f622ff548c572e0c03440b49b9531ff00e4ed5738b459f011e8"
             ],
+            "index": "pypi",
             "markers": "python_version >= '3.5'",
             "version": "==1.18.5"
         },