javac: use 'file' instead of 'filename' (#1945)

pages/common/javac.md

@@ -4,11 +4,11 @@
 
 - Compile a .java file:
 
-`javac {{filename.java}}`
+`javac {{file.java}}`
 
 - Compile several .java files:
 
-`javac {{filename1.java}} {{filename2.java}} {{filename3.java}}`
+`javac {{file1.java}} {{file2.java}} {{file3.java}}`
 
 - Compile all .java files in current directory:
 
@@ -16,4 +16,4 @@
 
 - Compile a .java file and place the resulting class file in a specific directory:
 
-`javac -d {{path/to/some/directory}} {{filename.java}}`
+`javac -d {{path/to/some/directory}} {{file.java}}`