[DOC] Specify shell format to shell commands

Merged: https://github.com/ruby/ruby/pull/7076

doc/contributing/building_ruby.md

@@ -22,19 +22,19 @@
 
 3. Checkout the CRuby source code:
 
-    ```
+    ``` shell
     git clone https://github.com/ruby/ruby.git
     ```
 
 4. Generate the configure file:
 
-    ```
+    ``` shell
     ./autogen.sh
     ```
 
 5. Create a `build` directory outside of the source directory:
 
-    ```
+    ``` shell
     mkdir build && cd build
     ```
 
@@ -42,13 +42,13 @@
 
 6. We'll install Ruby in `~/.rubies/ruby-master`, so create the directory:
 
-    ```
+    ``` shell
     mkdir ~/.rubies
     ```
 
 7. Run configure:
 
-    ```
+    ``` shell
     ../configure --prefix="${HOME}/.rubies/ruby-master"
     ```
 
@@ -56,7 +56,7 @@
 
 8. Build Ruby:
 
-    ```
+    ``` shell
     make install
     ```
 
@@ -89,7 +89,7 @@ about Ruby's build to help out.
 In GNU make and BSD make implementations, to run a specific make script in parallel, pass the flag `-j<number of processes>`. For instance,
 to run tests on 8 processes, use:
 
-```
+``` shell
 make test-all -j8
 ```
 
@@ -117,7 +117,7 @@ Miniruby is a version of Ruby which has no external dependencies and lacks certa
 It can be useful in Ruby development because it allows for faster build times. Miniruby is
 built before Ruby. A functional Miniruby is required to build Ruby. To build Miniruby:
 
-```
+``` shell
 make miniruby
 ```
 
@@ -151,7 +151,7 @@ On Linux it is important to specify `-O0` when debugging. This is especially tru
 
 You need to be able to use gcc (gcov) and lcov visualizer.
 
-```
+``` shell
 ./autogen.sh
 ./configure --enable-gcov
 make