Ruby indentation conventions

By convention, Ruby code is indented using two spaces (  ) per-level.
The code used tabs (\t) previously and therefore wasn't idiomatic.
This change updates the indenting to use two spaces.

spring-boot-cli/src/main/homebrew/springboot.rb

 require 'formula'
 
 class Springboot < Formula
-	homepage 'http://projects.spring.io/spring-boot/'
-	url 'https://repo.spring.io/${repo}/org/springframework/boot/spring-boot-cli/${project.version}/spring-boot-cli-${project.version}-bin.tar.gz'
-	version '${project.version}'
-	sha1 '${checksum}'
-	head 'https://github.com/spring-projects/spring-boot.git'
+  homepage 'http://projects.spring.io/spring-boot/'
+  url 'https://repo.spring.io/${repo}/org/springframework/boot/spring-boot-cli/${project.version}/spring-boot-cli-${project.version}-bin.tar.gz'
+  version '${project.version}'
+  sha1 '${checksum}'
+  head 'https://github.com/spring-projects/spring-boot.git'
 
-	if build.head?
-		depends_on 'maven' => :build
-	end
+  if build.head?
+    depends_on 'maven' => :build
+  end
 
-	def install
-		if build.head?
-			Dir.chdir('spring-boot-cli') { system 'mvn -U -DskipTests=true package' }
-			root = 'spring-boot-cli/target/spring-boot-cli-*-bin/spring-*'
-		else
-			root = '.'
-		end
+  def install
+    if build.head?
+      Dir.chdir('spring-boot-cli') { system 'mvn -U -DskipTests=true package' }
+      root = 'spring-boot-cli/target/spring-boot-cli-*-bin/spring-*'
+    else
+      root = '.'
+    end
 
-		bin.install Dir["#{root}/bin/spring"]
-		lib.install Dir["#{root}/lib/spring-boot-cli-*.jar"]
-		bash_completion.install Dir["#{root}/shell-completion/bash/spring"]
-		zsh_completion.install Dir["#{root}/shell-completion/zsh/_spring"]
-	end
+    bin.install Dir["#{root}/bin/spring"]
+    lib.install Dir["#{root}/lib/spring-boot-cli-*.jar"]
+    bash_completion.install Dir["#{root}/shell-completion/bash/spring"]
+    zsh_completion.install Dir["#{root}/shell-completion/zsh/_spring"]
+  end
 end