Dep/Boost: raise minimum requires boost version for Linux systems to 1.68

.travis.yml

@@ -14,7 +14,7 @@ addons:
       - sourceline: 'ppa:mhier/libboost-latest'
 #     - sourceline: 'ubuntu-toolchain-r-test'
     packages:
-      - boost1.67
+      - boost1.68
       - libssl-dev
       - libmysqlclient-dev
       - libreadline6-dev

dep/boost/CMakeLists.txt

@@ -40,7 +40,7 @@ if (WIN32)
   # On windows the requirements are higher according to the wiki.
   set(BOOST_REQUIRED_VERSION 1.70)
 else()
-  set(BOOST_REQUIRED_VERSION 1.67)
+  set(BOOST_REQUIRED_VERSION 1.68)
 endif()
 
 if (STD_HAS_WORKING_WREGEX)