Use lower-case letters for github URLs.

This makes it a little more consistent; now, "cretonne" is never capitalized
in identifier, path, or URL contexts. It is capitalized in natural
language contexts when referring to the project.

cranelift/filetests/regalloc/coalescing-207.cton

@@ -2,7 +2,7 @@ test regalloc
 set is_64bit
 isa x86 haswell
 
-; Reported as https://github.com/Cretonne/cretonne/issues/207
+; Reported as https://github.com/cretonne/cretonne/issues/207
 ;
 ; The coalescer creates a virtual register with two interfering values.
 function %pr207(i64 vmctx, i32, i32) -> i32 system_v {

cranelift/filetests/regalloc/coalescing-216.cton

@@ -2,7 +2,7 @@ test regalloc
 set is_64bit
 isa x86 haswell
 
-; Reported as https://github.com/Cretonne/cretonne/issues/216 from the Binaryen fuzzer.
+; Reported as https://github.com/cretonne/cretonne/issues/216 from the Binaryen fuzzer.
 ;
 ; The (old) coalescer creates a virtual register with two identical values.
 function %pr216(i32 [%rdi], i64 vmctx [%rsi]) -> i64 [%rax] system_v {

cranelift/filetests/regalloc/reload-208.cton

@@ -4,7 +4,7 @@ isa x86 haswell
 
 ; regex: V=v\d+
 
-; Filed as https://github.com/Cretonne/cretonne/issues/208
+; Filed as https://github.com/cretonne/cretonne/issues/208
 ;
 ; The verifier complains about a branch argument that is not in the same virtual register as the
 ; corresponding EBB argument.