fix mermaid unsupported feature

Author: CunliangGeng

docs/diagrams/arranger.md

@@ -5,15 +5,15 @@ The [DatasetArranger][nplinker.arranger.DatasetArranger] is implemented accordin
 ## Strain mappings file
 ``` mermaid
 flowchart TD
-    StrainMappings[`strain_mappings.json`] --> SM{Is the mode PODP?}
+    StrainMappings[strain_mappings.json] --> SM{Is the mode PODP?}
     SM --> |No |SM0[Validate the file]
     SM --> |Yes|SM1[Generate the file] --> SM0
 ```
 
 ## Strain selection file
 ``` mermaid
 flowchart TD
-    StrainsSelected[`strains_selected.json`] --> S{Does the file exist?}
+    StrainsSelected[strains_selected.json] --> S{Does the file exist?}
     S --> |No | S0[Nothing to do]
     S --> |Yes| S1[Validate the file]
 ```