Bump pipenv version

bin/steps/pipenv

@@ -41,7 +41,7 @@ if [ ! "$SKIP_PIPENV_INSTALL" ]; then
             export PIP_EXTRA_INDEX_URL
         fi
 
-        export PIPENV_VERSION="11.8.2"
+        export PIPENV_VERSION="2018.5.18"
 
         # Install pipenv.
         /app/.heroku/python/bin/pip install pipenv==$PIPENV_VERSION --upgrade &> /dev/null

test/fixtures/pipenv-lock/Pipfile.lock

 {
     "_meta": {
         "hash": {
-            "sha256": "397f2c55e3558ea57d292e3fc19b34e483770e5ec02cdedfb1f330680cd26635"
-        },
-        "host-environment-markers": {
-            "implementation_name": "cpython",
-            "implementation_version": "3.6.3",
-            "os_name": "posix",
-            "platform_machine": "x86_64",
-            "platform_python_implementation": "CPython",
-            "platform_release": "16.7.0",
-            "platform_system": "Darwin",
-            "platform_version": "Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64",
-            "python_full_version": "3.6.3",
-            "python_version": "3.6",
-            "sys_platform": "darwin"
+            "sha256": "09ad9dcae1870ba083f43c5a05ed8943b23bd4c27e61a13ecf4e16d18500ad98"
         },
         "pipfile-spec": 6,
         "requires": {},
         "sources": [
             {
                 "name": "pypi",
-                "url": "https://pypi.python.org/simple",
+                "url": "https://pypi.org/simple",
                 "verify_ssl": true
             }
         ]
@@ -29,22 +16,23 @@
     "default": {
         "delegator.py": {
             "hashes": [
-                "sha256:2575c4adc923ad0b8fdaa433f862b2b7cf21982717fb23cc895fd8f249ea820c",
-                "sha256:495e11ada66648650171a6c9a188df4eb050b235abff8771f41ee8a064eb9ded"
+                "sha256:2d46966a7f484d271b09e2646eae1e9acadc4fdf2cb760c142f073e81c927d8d",
+                "sha256:58f3ea6fe36680e1d828e2e66e52844b826f186409dfee4436e42351b0e699fe"
             ],
-            "version": "==0.0.13"
+            "index": "pypi",
+            "version": "==0.1.0"
         },
         "pexpect": {
             "hashes": [
-                "sha256:f853b52afaf3b064d29854771e2db509ef80392509bde2dd7a6ecf2dfc3f0018",
-                "sha256:3d132465a75b57aa818341c6521392a06cc660feb3988d7f1074f39bd23c9a92"
+                "sha256:9783f4644a3ef8528a6f20374eeb434431a650c797ca6d8df0d81e30fffdfa24",
+                "sha256:9f8eb3277716a01faafaba553d629d3d60a1a624c7cf45daa600d2148c30020c"
             ],
-            "version": "==4.2.1"
+            "version": "==4.5.0"
         },
         "ptyprocess": {
             "hashes": [
-                "sha256:e8c43b5eee76b2083a9badde89fd1bbce6c8942d1045146e100b7b5e014f4f1a",
-                "sha256:e64193f0047ad603b71f202332ab5527c5e52aa7c8b609704fc28c0dc20c4365"
+                "sha256:e64193f0047ad603b71f202332ab5527c5e52aa7c8b609704fc28c0dc20c4365",
+                "sha256:e8c43b5eee76b2083a9badde89fd1bbce6c8942d1045146e100b7b5e014f4f1a"
             ],
             "version": "==0.5.2"
         }