ci: use $HOME variable rather than /home/travis

Author: tommilligan

ci/run.sh

@@ -9,7 +9,7 @@ export LD_LIBRARY_PATH="$HOME/lib"
 which protoc
 protoc --version
 if [ -z "$ON_WINDOWS" ];
-    then PKG_CONFIG_PATH="/home/travis/lib/pkgconfig" interop/cxx/compile.sh
+    then PKG_CONFIG_PATH="$HOME/lib/pkgconfig" interop/cxx/compile.sh
 fi
 export RUST_BACKTRACE=1