Require clang >= 3.6 as 3.5 is failing on debug symbol generation

.travis.yml

@@ -18,7 +18,7 @@ before_install:
 install:
   - if [ $TRAVIS_OS_NAME = linux ]; then
       if [ "$CXX" = "clang++" ]; then
-        export CXX=clang++-3.5;
+        export CXX=clang++-3.6;
       elif [ "$CXX" = "g++" ]; then
         export CXX=g++-5;
       fi;
@@ -34,9 +34,9 @@ addons:
     sources:
       - boost-latest
       - ubuntu-toolchain-r-test
-      - llvm-toolchain-precise-3.5
+      - llvm-toolchain-precise-3.6
     packages:
-      - clang-3.5
+      - clang-3.6
       - libstdc++-5-dev
       - g++-5
       - libncursesw5-dev

README.asciidoc

@@ -102,7 +102,7 @@ Building
 
 Kakoune dependencies are:
 
- * A {cpp}14 compliant compiler (GCC >= 5 or clang >= 3.5) along with its
+ * A {cpp}14 compliant compiler (GCC >= 5 or clang >= 3.6) along with its
    associated {cpp} standard library (libstdc{pp} or libc{pp})
  * boost (>= 1.50)
  * ncurses with wide-characters support (>= 5.3, generally referred to as libncursesw)