TravisCI: Fix fetching of xapian-bindings (issue2550931)

The server that hosts the xapian-bindings file is now serving them up
via HTTPS, but for some reason wget doesn't like the certificate, while
curl has no problems.

Revert the previous attempts to fix this problem and replace the use of
wget with curl seems to resolve the problem

Author: jerrykan

.travis.yml

@@ -12,12 +12,10 @@ addons:
       # Required to install pyme
       - libgpgme11-dev
       - swig
-      # allow wget to pull https url's
-      - ca-certificates
 
 before_install:
   - cd /tmp
-  - wget -q --ca-certificate $TRAVIS_BUILD_DIR/tools/lets-encrypt-x3-cross-signed.pem https://oligarchy.co.uk/xapian/1.2.8/xapian-bindings-1.2.8.tar.gz
+  - curl -s -O https://oligarchy.co.uk/xapian/1.2.8/xapian-bindings-1.2.8.tar.gz
   - tar -zxvf xapian-bindings-1.2.8.tar.gz
   - cd xapian-bindings-1.2.8/
   - ./configure --prefix=$VIRTUAL_ENV --with-python && make && make install