Remove cache of Dockerfile

fix: Remove english shell dependency in manage.sh script

see https://github.com/asciimoo/searx/pull/1479#issuecomment-569904632Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

This reverts commit 7b9c8f77.

[fix] ffox useragent: use Windows NT 10.0 and not Windows NT 10

This is an addittion to PR #1934:

  The .0 change really counts on some engines like Bing which seems to allow
  Windows NT 10.0 but not Windows NT 10.
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

Update default user agents

Remove discontinued faroo engine

[fix] remove usage of request context where not available

[Fix] Startpage ValueError on Spanish date format

[mod] requirements.txt: upgrade dependency versions.

[add] Additional Wikimedia projects

[add] rubygems engine

[mod] .travis.yml: add Python 3.7 and Python 3.8

Suggested by @Venca24 <https://github.com/asciimoo/searx/pull/1914#issuecomment-610194209>.

A list of the added projects:
- Wikibooks
- Wikinews
- Wikiquote
- Wikisource
- Wiktionary
- Wikiversity
- Wikivoyage

improve travis build

BTW: separate env output in the travis log
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

[fix] travis: fix docker tag.

the "-dirty" ignores the searx/brand.py and utils/brand.env files.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>