Fixed readme syntax (#445)

Signed-off-by: Alejandro Hernández Cordero <[email protected]>

README.md

@@ -32,7 +32,7 @@ For a complete list of commands run `gz fuel -h` on the command line.
 
 **List all models**
 
-```{.sh}
+```bash
 $ gz fuel list -t model -r | head
 https://fuel.gazebosim.org/anonymous/test_model_595389531
 https://fuel.gazebosim.org/anonymous/test_model_122023392
@@ -48,7 +48,7 @@ https://fuel.gazebosim.org/anonymous/test_model_380348669
 
 **Download a model**
 
-```{.sh}
+```bash
 $ gz fuel download -u https://fuel.gazebosim.org/1.0/OpenRobotics/models/Ambulance -v 4
 Downloading model:
   Name: Ambulance
@@ -101,14 +101,14 @@ Create a private token at
 [https://app.gazebosim.org/settings#access_tokens](https://app.gazebosim.org/settings#access_tokens). Store the generated token someplace safe.
 
 The private token can then be used to upload a model:
-```{.sh}
+```bash
 gz fuel upload -m ~/path_to_model --header 'Private-token: <TOKEN>'
 ```
 
 ## Dependencies
 On ubuntu run
 
-```{.sh}
+```bash
 sudo apt install ruby-ffi libzip-dev libcurl-dev libjsoncpp-dev
 ```