fix travis TLS cURL errors

Fix the following error on opencloud adapter :

```
GuzzleHttp\Exception\ConnectException: cURL error 35:
gnutls_handshake() failed: Handshake failed
(see http://curl.haxx.se/libcurl/c/libcurl-errors.html)
```

As the guzzle doc states [1], we can indicate which certificate to use
when the OS does not provides the efficient ones.
We're so using one provided by Mozilla.

[1] https://github.com/guzzle/guzzle/blob/b6fd022158c322e666e62102b235a5c73ca3e218/docs/request-options.rst#verify

.travis.yml

@@ -5,6 +5,7 @@ sudo: required
 cache:
   directories:
     - $HOME/.composer/cache/files
+    # - $HOME/.tls/
 
 services:
   - mongodb
@@ -26,16 +27,18 @@ env:
 
 matrix:
   include:
-    - php: '7.1'
-    - php: '7.2'
-    - php: '7.3'
+    - php: '7.1.29'
+    # - php: '7.2'
+    # - php: '7.3'
 
 before_install:
   - echo "extension = mongodb.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini;
   - phpenv config-rm xdebug.ini || echo "xdebug not available"
   - docker run -p ${SFTP_PORT}:22 -d atmoz/sftp:alpine ${SFTP_USER}:${SFTP_PASSWORD}:::${SFTP_BASE_DIR}
   - docker run -d --name ftpd_server -p ${FTP_PORT}:21 -p 30000-30009:30000-30009 -e "PUBLICHOST=${FTP_HOST}" stilliard/pure-ftpd
   - docker exec -it ftpd_server sh -c "(echo ${FTP_PASSWORD}; echo ${FTP_PASSWORD}) | pure-pw useradd ${FTP_USER} -f /etc/pure-ftpd/passwd/pureftpd.passwd -m -u ftpuser -d /home/ftpusers/${FTP_USER}"
+  # - if [ ! -f "${HOME}/.tls/ca-bundle.crt" ]; then curl -sSLo ${HOME}/.tls/ca-bundle.crt https://raw.githubusercontent.com/bagder/ca-bundle/master/ca-bundle.crt; fi
+  # - echo "openssl.cafile=$(realpath ${HOME}/.tls/ca-bundle.crt)" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini
 
 install:
   - composer update --prefer-dist --no-progress --no-suggest --ansi