Update ci scripts to build with mruby 1.2.0, 1.3.0 and head

Author: katzer

.appveyor.yml

@@ -28,6 +28,8 @@ environment:
     VCVARSALL: C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat
     CC: gcc
   matrix:
+  - MRUBY_VERSION: 1.2.0
+    COMPILER: C:\MinGW # MinGW 32-bit 5.3.0
   - MRUBY_VERSION: 1.3.0
     COMPILER: C:\MinGW # MinGW 32-bit 5.3.0
   - MRUBY_VERSION: head

.travis.yml

@@ -25,6 +25,7 @@ compiler:
 - clang
 
 env:
+- MRUBY_VERSION=1.2.0
 - MRUBY_VERSION=1.3.0
 - MRUBY_VERSION=head