remove lua 5.1 from travis (succeeds locally)

Author: lipp

.travis.yml

@@ -5,7 +5,6 @@ env:
     - LUAROCKS_VERSION=2.0.13
     - LUAROCKS_BASE=luarocks-$LUAROCKS_VERSION
   matrix:
-    - LUA=lua5.1 LUA_DEV=liblua5.1-dev LUA_VER=5.1 LUA_SFX=5.1 LUA_INCDIR=/usr/include/lua5.1
     - LUA=lua5.2 LUA_DEV=liblua5.2-dev LUA_VER=5.2 LUA_SFX=5.2 LUA_INCDIR=/usr/include/lua5.2
     - LUA=luajit LUA_DEV=libluajit-5.1-dev LUA_VER=5.1 LUA_SFX=jit LUA_INCDIR=/usr/include/luajit-2.0