corrected a typo.

Git/git-book.md

@@ -161,14 +161,14 @@ $ git config --list
 * creating a lightweight tag: `$ git tag v1.4-lw`
 * show information about a tag: `$ git show v1.4`
 * You can tag after other commits have been made:
-  ```
-  $ git log --pretty=oneline
-  15027957951b64cf874c3557a0f3547bd83b3ff6 Merge branch 'experiment'
-  a6b4c97498bd301d84096da251c98a07c7723e65 beginning write support
-  0d52aaab4479697da7686c15f77a3d64d9165190 one more thing
+```
+$ git log --pretty=oneline
+15027957951b64cf874c3557a0f3547bd83b3ff6 Merge branch 'experiment'
+a6b4c97498bd301d84096da251c98a07c7723e65 beginning write support
+0d52aaab4479697da7686c15f77a3d64d9165190 one more thing
 
-  $ git tag -a v1.2 a6b4c9
-  ```
+$ git tag -a v1.2 a6b4c9
+```
 * sharing tags with remotes: `$ git push origin v1.5`
 * to push all tags at once: `$ git push origin --tags`
 * You can't check out tags in git. You must checkout a branch at a specific tag: