Update .travis.yml (MacPython#142)

Author: lithomas1

.travis.yml

@@ -25,8 +25,8 @@ jobs:
     - os: linux
       env:
         - MB_PYTHON_VERSION=3.7
-        - NP_BUILD_DEP="numpy==1.17.3"
-        - NP_TEST_DEP="numpy==1.17.3"
+        - NP_BUILD_DEP="numpy==1.19.1"
+        - NP_TEST_DEP="numpy==1.19.1"
     - os: linux
       env:
         - MB_PYTHON_VERSION=3.8