Improve code in Readme

This patch makes the code in readme valid. The previous code had a few typos.
diff --git a/README.md b/README.md
index db20817..d9e3327 100644
--- a/README.md
+++ b/README.md
@@ -198,17 +198,17 @@
 Then in my tests I would initialize a new MemMapFs for each test:
 ```go
 func TestExist(t *testing.T) {
-	appFS = afero.NewMemMapFs()
+	appFS := afero.NewMemMapFs()
 	// create test files and directories
-	appFS.MkdirAll("src/a", 0755))
+	appFS.MkdirAll("src/a", 0755)
 	afero.WriteFile(appFS, "src/a/b", []byte("file b"), 0644)
 	afero.WriteFile(appFS, "src/c", []byte("file c"), 0644)
-	_, err := appFS.Stat("src/c")
+	name := "src/c"
+	_, err := appFS.Stat(name)
 	if os.IsNotExist(err) {
-        t.Errorf("file \"%s\" does not exist.\n", name)
+		t.Errorf("file \"%s\" does not exist.\n", name)
 	}
 }
-
 ```
 
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