ci: Travis: include pexpect in main py37 job

This removes xdist there (not compatible with the pexpect tests), but it
is better to have one job less, although slower due to not using xdist.

.travis.yml

@@ -39,8 +39,13 @@ jobs:
 
     # Full run of latest supported version, without xdist.
     # Coverage for:
+    # - pytester's LsofFdLeakChecker
+    # - TestArgComplete (linux only)
+    # - numpy
+    # - old attrs
+    # - verbose=0
     # - test_sys_breakpoint_interception (via pexpect).
-    - env: TOXENV=py37-pexpect PYTEST_COVERAGE=1
+    - env: TOXENV=py37-lsof-numpy-oldattrs-pexpect-twisted PYTEST_COVERAGE=1 PYTEST_ADDOPTS=
       python: '3.7'
 
     # Coverage tracking is slow with pypy, skip it.
@@ -50,14 +55,6 @@ jobs:
     - env: TOXENV=py35-xdist
       python: '3.5'
 
-    # Coverage for:
-    # - pytester's LsofFdLeakChecker
-    # - TestArgComplete (linux only)
-    # - numpy
-    # - old attrs
-    # - verbose=0
-    - env: TOXENV=py37-lsof-oldattrs-numpy-twisted-xdist PYTEST_COVERAGE=1 PYTEST_ADDOPTS=
-
     # Specialized factors for py37.
     - env: TOXENV=py37-pluggymaster-xdist
     - env: TOXENV=py37-freeze