Update README.md

Author: minoue-xx

README.md

@@ -62,7 +62,7 @@ save('sampleData.mat','sampleData');
 # References
 
 
-[1] Bechhoefer, Eric, Brandon Van Hecke, and David He. 2013. “Processing for Improved Spectral Analysis”. Annual Conference of the PHM Society 5 (1). https://doi.org/10.36001/phmconf.2013.v5i1.2220.
+[1] Bechhoefer, Eric, Brandon Van Hecke, and David He. 2013. “Processing for Improved Spectral Analysis”. Annual Conference of the PHM Society 5 (1)
 
 # Helper Function