travis: use Makefile target travis.codecov to install codecov

fix travis build error [1]::

  The command "local/py3/bin/pip install codecov" failed and exited with 127

Use the correct pip (python environment) from build environment::

  $(PY_ENV_BIN)/python -m pip

[1] https://travis-ci.org/github/asciimoo/searx/jobs/669701405#L590Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

.travis.yml

@@ -14,7 +14,7 @@ install:
   - make V=1 install
   - make V=1 gecko.driver
   - make V=1 node.env
-  - local/py3/bin/pip install codecov
+  - make V=1 travis.codecov
 script:
   - make V=1 themes
   - make V=1 test

Makefile

@@ -220,4 +220,11 @@ test.clean:
 	@echo "CLEAN     intermediate test stuff"
 	$(Q)rm -rf geckodriver.log .coverage coverage/
 
+
+# travis
+# ------
+
+travis.codecov:
+	$(Q)$(PY_ENV_BIN)/python -m pip install codecov
+
 .PHONY: $(PHONY)