Travis uses Pipfile instead of re-specifying deps

.travis.yml

@@ -2,7 +2,7 @@ sudo: required
 dist: trusty
 language: c
 python:
-  - "3.5"
+  - "3.6"
 cache:
   apt: true
   directories:
@@ -33,14 +33,12 @@ before_install:
   - pyenv global 3.6
   - sudo apt-get install python3-pip
   - sudo pip3 install --upgrade pip
-  - python --version
-  - python3 --version
+  - pip3 install --user pipenv
 install:
   - install_uncrustify
   - install_pg
   - install_custom_pg
-  - pip3 install --user mitmproxy==4.0.4
-  - pip3 install --user construct==2.9.45
+  - PIPENV_PIPFILE="${TRAVIS_BUILD_DIR}"/src/test/regress/Pipfile pipenv install --system --deploy
   - mitmproxy --version
   # download and install HLL and TopN manually, as custom builds won't satisfy deps
   # only install if performing non-11 build

src/test/regress/Pipfile

@@ -5,7 +5,7 @@ verify_ssl = true
 
 [packages]
 mitmproxy = "==4.0.4"
-construct = "*"
+construct = "==2.9.45"
 
 [dev-packages]
 

src/test/regress/Pipfile.lock

@@ -1,19 +1,19 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "3286c9e0c4c77c82a7e1edb2f15f57044889b13497909910887b82cfb90977fc"
+            "sha256": "1d99f17bd98cc90bbebdf6da999b3d82e1530ba5dbbeeceaf50cf090b78bbd12"
         },
         "host-environment-markers": {
             "implementation_name": "cpython",
-            "implementation_version": "3.5.2",
+            "implementation_version": "3.6.6",
             "os_name": "posix",
             "platform_machine": "x86_64",
             "platform_python_implementation": "CPython",
             "platform_release": "4.4.0-130-generic",
             "platform_system": "Linux",
             "platform_version": "#156-Ubuntu SMP Thu Jun 14 08:53:28 UTC 2018",
-            "python_full_version": "3.5.2",
-            "python_version": "3.5",
+            "python_full_version": "3.6.6",
+            "python_version": "3.6",
             "sys_platform": "linux"
         },
         "pipfile-spec": 6,