Revert "do not install libcurl for linux"

This reverts commit 031a219.

Author: mschenk42

.travis.yml

@@ -8,7 +8,7 @@ go:
   - "1.10"
 
 before_install:
-  # - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then sudo apt-get install -y curl libcurl3 libcurl3-gnutls libcurl4-gnutls-dev; fi
+  - if [ "${TRAVIS_OS_NAME}" == "linux" ]; then sudo apt-get install -y curl libcurl3 libcurl3-gnutls libcurl4-gnutls-dev; fi
   - sudo apt-get remove libssl-dev || true
   - $GOPATH/src/github.com/git-time-metric/gtm/script/git2go-init.sh
   - cd $GOPATH/src/github.com/libgit2/git2go