Use `colorize` helper for `require_gcc`

Ensures that color is off if the stderr stream is not a terminal

bin/ruby-build

@@ -595,15 +595,16 @@ require_gcc() {
   local gcc="$(locate_gcc || true)"
 
   if [ -z "$gcc" ]; then
-    local esc=$'\033'
     { echo
-      echo "${esc}[1mERROR${esc}[0m: This package must be compiled with GCC, but ruby-build couldn't"
+      colorize 1 "ERROR"
+      echo ": This package must be compiled with GCC, but ruby-build couldn't"
       echo "find a suitable \`gcc\` executable on your system. Please install GCC"
       echo "and try again."
       echo
 
       if [ "$(uname -s)" = "Darwin" ]; then
-        echo "${esc}[1mDETAILS${esc}[0m: Apple no longer includes the official GCC compiler with Xcode"
+        colorize 1 "DETAILS"
+        echo ": Apple no longer includes the official GCC compiler with Xcode"
         echo "as of version 4.2. Instead, the \`gcc\` executable is a symlink to"
         echo "\`llvm-gcc\`, a modified version of GCC which outputs LLVM bytecode."
         echo
@@ -613,15 +614,19 @@ require_gcc() {
         echo "GCC compiler installed on your system."
         echo
 
+        colorize 1 "TO FIX THE PROBLEM"
         if type brew &>/dev/null; then
-          echo "${esc}[1mTO FIX THE PROBLEM${esc}[0m: Install Homebrew's apple-gcc42 package with this"
-          echo "command: ${esc}[4mbrew tap homebrew/dupes ; brew install apple-gcc42${esc}[0m"
+          echo ": Install Homebrew's apple-gcc42 package with this"
+          echo -n "command: "
+          colorize 4 "brew tap homebrew/dupes ; brew install apple-gcc42"
         else
-          echo "${esc}[1mTO FIX THE PROBLEM${esc}[0m: Install the official GCC compiler using these"
-          echo "packages: ${esc}[4mhttps://github.com/kennethreitz/osx-gcc-installer/downloads${esc}[0m"
+          echo ": Install the official GCC compiler using these"
+          echo -n "packages: "
+          colorize 4 "https://github.com/kennethreitz/osx-gcc-installer/downloads"
         fi
 
         echo
+        echo
         echo "You will need to install the official GCC compiler to build older"
         echo "versions of Ruby even if you have installed Apple's Command Line Tools"
         echo "for Xcode package. The Command Line Tools for Xcode package only"