fix issues in mkdocs.yml

mkdocs.yml

@@ -6,6 +6,7 @@ nav:
       - Introduction: introduction.md
       - Common principles: common-principles.md
       - Modality agnostic files: modality-agnostic-files.md
+      - Modality agnostic files:
           - Magnetic Resonance Imaging: modality-specific-files/magnetic-resonance-imaging-data.md
           - Magnetoencephalography: modality-specific-files/magnetoencephalography.md
           - Electroencephalography: modality-specific-files/electroencephalography.md
@@ -96,6 +97,8 @@ extra_javascript:
 markdown_extensions:
   - toc:
       anchorlink: true
+  - pymdownx.superfences
+plugins:
   - search
   - branchcustomization:
       update_config:
@@ -120,7 +123,6 @@ markdown_extensions:
         "04-modality-specific-files/09-positron-emission-tomography.md": "modality-specific-files/positron-emission-tomography.md"
         "04-modality-specific-files/10-microscopy.md": "modality-specific-files/microscopy.md"
         "04-modality-specific-files/11-near-infrared-spectroscopy.md": "modality-specific-files/near-infrared-spectroscopy.md"
-        '04-modality-specific-files/12-eye-tracking.md': 'modality-specific-files/eye-tracking.md'
         "05-derivatives/01-introduction.md": "derivatives/introduction.md"
         "05-derivatives/02-common-data-types.md": "derivatives/common-data-types.md"
         "05-derivatives/03-imaging.md": "derivatives/imaging.md"