Travis CI: more fun with yaml and quoting

.travis.yml

@@ -17,7 +17,7 @@ addons:
 before_install:
   - mkdir ext
   - git clone --recursive --depth=1 --single-branch --branch boost-1.64.0 git://github.com/boostorg/boost ext/boost
-  - cd ext/boost && ./bootstrap.sh --prefix=$TRAVIS_BUILD_DIR/ext && ./b2 headers && echo 'using clang : 4.0 : clang++-4.0 ;' >> project-config.jam && ./b2 -j4 --with-thread --with-date_time --with-system --with-program_options --with-signals --with-serialization --with-chrono --with-test --with-context --with-locale toolset=clang link=shared install
+  - "cd ext/boost && ./bootstrap.sh --prefix=$TRAVIS_BUILD_DIR/ext && ./b2 headers && echo 'using clang : 4.0 : clang++-4.0 ;' >> project-config.jam && ./b2 -j4 --with-thread --with-date_time --with-system --with-program_options --with-signals --with-serialization --with-chrono --with-test --with-context --with-locale toolset=clang link=shared install"
   - cd $TRAVIS_BUILD_DIR/ext && git clone --depth=1 --single-branch git://github.com/cryptonomex/secp256k1-zkp
   - cd secp256k1-zkp && ./autogen.sh && ./configure --prefix=$TRAVIS_BUILD_DIR/ext CC=clang-4.0 CXX=clang++-4.0 && make && make install
 script: