For Travis CI - install 32-bit readline software package.

.travis.yml

@@ -54,7 +54,7 @@ matrix:
       compiler: clang-64bit-shared
     - &Linux-32bit
       compiler: gcc-32bit-static
-      addons: {apt: {sources: *default_sources, packages: [*linux_packages, g++-multilib, "libxrandr-dev:i386", "libglapi-mesa:i386", "libgl1-mesa-glx:i386", "libgl1-mesa-dev:i386", "libxext-dev:i386", "libxrender-dev:i386"]}}
+      addons: {apt: {sources: *default_sources, packages: [*linux_packages, g++-multilib, "libxrandr-dev:i386", "libglapi-mesa:i386", "libgl1-mesa-glx:i386", "libgl1-mesa-dev:i386", "libxext-dev:i386", "libxrender-dev:i386", lib32readline6-dev]}}
       env: LINUX=1 URHO3D_LIB_TYPE=STATIC URHO3D_64BIT=0
     - &Linux-32bit-shared
       <<: *Linux-32bit