Fix depwarns under 0.7 and bump REQUIRE and CI to 0.6. (#15)

Author: Sacha0

.travis.yml

@@ -3,8 +3,7 @@ os:
     - linux
     - osx
 julia:
-    - 0.4
-    - 0.5
+    - 0.6
     - nightly
 notifications:
     email: false

REQUIRE

@@ -1,2 +1,2 @@
-julia 0.4
+julia 0.6
 Compat 0.8.0

src/LaTeXStrings.jl

@@ -12,7 +12,7 @@ import Compat.String
 # \\beta\$".  To simplify this, we add a new string type with a macro
 # constructor, so that one can simply do L"$\alpha + \beta$".
 
-immutable LaTeXString <: AbstractString
+struct LaTeXString <: AbstractString
     s::String
 end