update debian:jessie python test to debian:stretch

Summary:
debian:jessie does not include an automatic way to install python3.5, which is needed by the latest version of numpy.
https://circleci.com/gh/facebookresearch/fastText/1522

adding debian:stretch test instead.

Reviewed By: EdouardGrave

Differential Revision: D17051945

fbshipit-source-id: 971e4d75008fcd5aa71c942b33c5a81f131db035

.circleci/config.yml

@@ -129,18 +129,19 @@ jobs:
             . .circleci/setup_debian.sh
             . .circleci/cmake_test.sh
 
-  "debian-jessie-gcc":
+  "debian-stretch-python":
     docker:
-      - image: debian:jessie
+      - image: debian:stretch
     working_directory: ~/repo
     steps:
       - checkout
       - run:
           command: |
             . .circleci/setup_debian.sh
-            . .circleci/gcc_test.sh
+            pip install .
+            python runtests.py -u
 
-  "debian-jessie-cmake":
+  "debian-jessie-gcc":
     docker:
       - image: debian:jessie
     working_directory: ~/repo
@@ -149,9 +150,9 @@ jobs:
       - run:
           command: |
             . .circleci/setup_debian.sh
-            . .circleci/cmake_test.sh
+            . .circleci/gcc_test.sh
 
-  "debian-jessie-python":
+  "debian-jessie-cmake":
     docker:
       - image: debian:jessie
     working_directory: ~/repo
@@ -160,8 +161,7 @@ jobs:
       - run:
           command: |
             . .circleci/setup_debian.sh
-            pip install .
-            python runtests.py -u
+            . .circleci/cmake_test.sh
 
   "website-build":
     docker: