Fix typos in "Project Structure" chapter.
Fix typos in "Project Structure" chapter.

JetBrains/intellij-sdk-docs,JetBrains/intellij-sdk-docs,artspb/intellij-sdk-docs,JetBrains/intellij-sdk-docs,artspb/intellij-sdk-docs,artspb/intellij-sdk-docs,artspb/intellij-sdk-docs