CI/Travis: upgrade to boost 1.67 and Ubuntu 18.4

.travis.yml

@@ -1,5 +1,5 @@
 sudo: false
-dist: trusty
+dist: bionic
 
 language: cpp
 compiler:
@@ -11,23 +11,17 @@ git:
 addons:
   apt:
     sources:
-      - ubuntu-toolchain-r-test
-      - sourceline: 'ppa:kzemek/boost'
+      - sourceline: 'ppa:mhier/libboost-latest'
+#     - sourceline: 'ubuntu-toolchain-r-test'
     packages:
-      - g++-6
-      - libboost1.58-dev
-      - libboost-filesystem1.58-dev
-      - libboost-iostreams1.58-dev
-      - libboost-program-options1.58-dev
-      - libboost-regex1.58-dev
-      - libboost-system1.58-dev
-      - libboost-thread1.58-dev
+      - boost1.67
       - libssl-dev
       - libmysqlclient-dev
       - libreadline6-dev
       - zlib1g-dev
       - libbz2-dev
       - libzmq3-dev
+      - g++-6
 
 services:
   - mysql