ci: work around rust-lang/cargo#3340

Author: Jorge Aparicio

.travis.yml

@@ -28,7 +28,10 @@ matrix:
     - env: TARGET=thumbv7m-none-eabi
     - env: TARGET=x86_64-apple-darwin
       os: osx
-env: TARGET=x86_64-unknown-linux-gnu
+env:
+  global:
+    - TARGET=x86_64-unknown-linux-gnu
+    - SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt
 
 before_install:
   - test "$TRAVIS_OS_NAME" = "osx" || docker run --rm --privileged multiarch/qemu-user-static:register

ci/run-docker.sh

@@ -18,6 +18,7 @@ run() {
            --user $(id -u):$(id -g) \
            -e CARGO_HOME=/cargo \
            -e CARGO_TARGET_DIR=/target \
+           -e SSL_CERT_FILE=$SSL_CERT_FILE \
            -v $HOME/.cargo:/cargo \
            -v `pwd`/target:/target \
            -v `pwd`:/checkout:ro \